diff --git a/build_support/catalog/test_update.py b/build_support/catalog/test_update.py
index 2e0e402ad..dc540ccba 100644
--- a/build_support/catalog/test_update.py
+++ b/build_support/catalog/test_update.py
@@ -747,6 +747,112 @@ def test_no_list_table_in_output(self, tmp_path, monkeypatch):
         assert ".. contents::" not in rst
 
 
+# ---------------------------------------------------------------------------
+# Tests for clean_stale_img_files
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.catalog_update
+class TestCleanStaleImgFiles:
+    """Tests for ``clean_stale_img_files(catalog_dir)``.
+
+    All tests construct a temporary catalog directory with hand-crafted game
+    files and img/ contents so they are completely isolated from the real
+    catalog on disk.
+    """
+
+    def _make_catalog(self, tmp_path):
+        """Return a minimal catalog dir with an img/ subdirectory."""
+        catalog_dir = tmp_path / "catalog"
+        (catalog_dir / "img").mkdir(parents=True)
+        (catalog_dir / "img" / ".gitkeep").touch()
+        return catalog_dir
+
+    def test_stale_file_is_removed(self, tmp_path):
+        """A file in img/ with no matching game file is deleted."""
+        catalog_dir = self._make_catalog(tmp_path)
+        stale = catalog_dir / "img" / "oldgame.png"
+        stale.touch()
+        update.clean_stale_img_files(catalog_dir)
+        assert not stale.exists()
+
+    def test_gitkeep_is_preserved(self, tmp_path):
+        """The .gitkeep sentinel is never removed, even when nothing else is kept."""
+        catalog_dir = self._make_catalog(tmp_path)
+        (catalog_dir / "img" / "oldgame.png").touch()
+        update.clean_stale_img_files(catalog_dir)
+        assert (catalog_dir / "img" / ".gitkeep").exists()
+
+    def test_expected_efg_files_are_kept(self, tmp_path):
+        """Image files that correspond to a current EFG game are not removed."""
+        catalog_dir = self._make_catalog(tmp_path)
+        (catalog_dir / "src").mkdir()
+        (catalog_dir / "src" / "game.efg").touch()
+        for ext in ["ef", "tex", "png", "pdf", "svg"]:
+            (catalog_dir / "img" / f"src/game.{ext}").parent.mkdir(parents=True, exist_ok=True)
+            (catalog_dir / "img" / f"src/game.{ext}").touch()
+        update.clean_stale_img_files(catalog_dir)
+        for ext in ["ef", "tex", "png", "pdf", "svg"]:
+            assert (catalog_dir / "img" / f"src/game.{ext}").exists()
+
+    def test_expected_nfg_files_are_kept(self, tmp_path):
+        """Image files for an NFG game (no .ef) are not removed."""
+        catalog_dir = self._make_catalog(tmp_path)
+        (catalog_dir / "src").mkdir()
+        (catalog_dir / "src" / "matrix.nfg").touch()
+        (catalog_dir / "img" / "src").mkdir()
+        for ext in ["tex", "png", "pdf", "svg"]:
+            (catalog_dir / "img" / f"src/matrix.{ext}").touch()
+        update.clean_stale_img_files(catalog_dir)
+        for ext in ["tex", "png", "pdf", "svg"]:
+            assert (catalog_dir / "img" / f"src/matrix.{ext}").exists()
+
+    def test_empty_directory_is_removed(self, tmp_path):
+        """A subdirectory of img/ that becomes empty after cleanup is also removed."""
+        catalog_dir = self._make_catalog(tmp_path)
+        stale_dir = catalog_dir / "img" / "oldgroup"
+        stale_dir.mkdir()
+        (stale_dir / "oldgame.png").touch()
+        update.clean_stale_img_files(catalog_dir)
+        assert not stale_dir.exists()
+
+    def test_nonempty_directory_is_kept(self, tmp_path):
+        """A subdirectory still containing expected files is not removed."""
+        catalog_dir = self._make_catalog(tmp_path)
+        (catalog_dir / "src").mkdir()
+        (catalog_dir / "src" / "game.efg").touch()
+        (catalog_dir / "img" / "src").mkdir()
+        for ext in ["ef", "tex", "png", "pdf", "svg"]:
+            (catalog_dir / "img" / f"src/game.{ext}").touch()
+        update.clean_stale_img_files(catalog_dir)
+        assert (catalog_dir / "img" / "src").is_dir()
+
+    def test_multi_variant_images_kept(self, tmp_path):
+        """Variant image files (e.g. {slug}__wide.*) are kept when the variant .ef exists."""
+        catalog_dir = self._make_catalog(tmp_path)
+        game_dir = catalog_dir / "src"
+        game_dir.mkdir()
+        (game_dir / "game.efg").touch()
+        (game_dir / "game.ef").touch()
+        (game_dir / "game__wide.ef").touch()  # triggers multi-variant
+        (catalog_dir / "img" / "src").mkdir()
+        for vkey in ["src/game", "src/game__wide"]:
+            for ext in ["ef", "tex", "png", "pdf", "svg"]:
+                p = catalog_dir / "img" / f"{vkey}.{ext}"
+                p.parent.mkdir(parents=True, exist_ok=True)
+                p.touch()
+        update.clean_stale_img_files(catalog_dir)
+        for vkey in ["src/game", "src/game__wide"]:
+            for ext in ["ef", "tex", "png", "pdf", "svg"]:
+                assert (catalog_dir / "img" / f"{vkey}.{ext}").exists()
+
+    def test_noop_when_img_absent(self, tmp_path):
+        """If catalog/img/ does not exist, the function returns without error."""
+        catalog_dir = tmp_path / "catalog"
+        catalog_dir.mkdir()
+        update.clean_stale_img_files(catalog_dir)  # must not raise
+
+
 # ---------------------------------------------------------------------------
 # Tests for update_makefile
 # ---------------------------------------------------------------------------
diff --git a/build_support/catalog/update.py b/build_support/catalog/update.py
index f61acc014..7dddd1394 100644
--- a/build_support/catalog/update.py
+++ b/build_support/catalog/update.py
@@ -313,6 +313,61 @@ def generate_rst_table(
         )
 
 
+def clean_stale_img_files(catalog_dir: Path | None = None) -> None:
+    """Remove files and directories from catalog/img/ with no corresponding current game.
+
+    Computes the set of expected image files from the game files currently in
+    *catalog_dir* (all .efg and .nfg files, respecting multi-variant .ef conventions),
+    then removes anything in catalog/img/ that is not in that set.  Preserves
+    .gitkeep.  Empty directories left behind by file removal are also removed.
+
+    This is useful after switching branches that reorganise or remove catalog games,
+    to prevent stale images from persisting alongside the updated catalog.
+    """
+    catalog_dir = catalog_dir or CATALOG_DIR
+    img_dir = catalog_dir / "img"
+    if not img_dir.is_dir():
+        return
+
+    # Build the set of expected image file paths from the current catalog contents.
+    expected_files: set[Path] = set()
+    game_files = [
+        p
+        for p in list(catalog_dir.rglob("*.efg")) + list(catalog_dir.rglob("*.nfg"))
+        if img_dir not in p.parents  # exclude generated copies already inside img/
+    ]
+    for game_file in game_files:
+        slug = game_file.relative_to(catalog_dir).with_suffix("").as_posix()
+        fmt = game_file.suffix.lstrip(".")  # "efg" or "nfg"
+        ef_variants = catalog_ef_file_variants(slug, catalog_dir) if fmt == "efg" else None
+        if ef_variants:
+            for variant in ef_variants:
+                for ext in ["ef", "tex", "png", "pdf", "svg"]:
+                    expected_files.add(img_dir / f"{variant['variant_key']}.{ext}")
+        else:
+            exts = (["ef"] if fmt == "efg" else []) + ["tex", "png", "pdf", "svg"]
+            for ext in exts:
+                expected_files.add(img_dir / f"{slug}.{ext}")
+
+    # Remove unexpected files (preserving .gitkeep).
+    removed = 0
+    for path in img_dir.rglob("*"):
+        if path.is_file() and path.name != ".gitkeep" and path not in expected_files:
+            path.unlink()
+            removed += 1
+
+    # Remove empty directories, deepest first.
+    for path in sorted(img_dir.rglob("*"), key=lambda p: len(p.parts), reverse=True):
+        if path.is_dir() and not any(path.iterdir()):
+            path.rmdir()
+            removed += 1
+
+    if removed:
+        print(f"Removed {removed} stale item(s) from {img_dir}")
+    else:
+        print(f"No stale files in {img_dir}")
+
+
 def update_makefile(
     catalog_dir: Path | None = None,
     am_path: Path | None = None,
@@ -390,6 +445,8 @@ def update_makefile(
     )
     args = parser.parse_args()
 
+    # Remove img/ files for games that no longer exist in the catalog.
+    clean_stale_img_files()
     # Create RST list-table used by doc/catalog.rst
     df = gbt.catalog.games(include_descriptions=True)
     generate_rst_table(df, CATALOG_RST_TABLE, regenerate_images=args.regenerate_images)
diff --git a/doc/developer.catalog.rst b/doc/developer.catalog.rst
index 68f0f442e..6c9cda489 100644
--- a/doc/developer.catalog.rst
+++ b/doc/developer.catalog.rst
@@ -104,7 +104,8 @@ Currently supported representations are:
 
    .. note::
 
-      You can use the ``--regenerate-images`` flag when building the docs locally for a second time to force any changes to be picked up.
+      - The ``pygambit.catalog`` module reads games directly from the repo's ``catalog/`` directory when working with an editable install of ``pygambit``.
+      - You can use the ``--regenerate-images`` flag when building the docs locally for a second time to force any changes to be picked up.
 
    .. warning::
 
diff --git a/src/pygambit/catalog.py b/src/pygambit/catalog.py
index 2b6aadaeb..ab759de93 100644
--- a/src/pygambit/catalog.py
+++ b/src/pygambit/catalog.py
@@ -7,13 +7,13 @@
 
 import pygambit as gbt
 
-# Use the full string path to where the catalog data are placed in the package
-_CATALOG_RESOURCE = files("pygambit") / "catalog_data"
-# This ensures that catalog files are included in editable installs too
-if not _CATALOG_RESOURCE.is_dir():
-    _repo_catalog = Path(__file__).parent.parent.parent / "catalog"
-    if _repo_catalog.is_dir():
-        _CATALOG_RESOURCE = _repo_catalog
+# Prefer the repo's live catalog/ directory when working in a development checkout.
+# This ensures changes to catalog/ are picked up immediately without reinstalling,
+# and avoids stale files in catalog_data/ left over from previous installs.
+# Fall back to the installed catalog_data/ only for deployed (non-development) packages,
+# where catalog/ does not exist relative to the installed source file.
+_repo_catalog = Path(__file__).parent.parent.parent / "catalog"
+_CATALOG_RESOURCE = _repo_catalog if _repo_catalog.is_dir() else files("pygambit") / "catalog_data"
 
 READERS = {
     ".nfg": gbt.read_nfg,