diff --git a/bricks/_common/common.mk b/bricks/_common/common.mk
index da7235863..4f7eea3e5 100644
--- a/bricks/_common/common.mk
+++ b/bricks/_common/common.mk
@@ -679,9 +679,16 @@ else
 FW_SECTIONS :=
 endif
 
-$(BUILD)/pbio_image_media.c $(BUILD)/pb_type_image_attributes.c: $(MEDIA_CONVERT)
+# Force rebuild if list of media sources changed.
+-include $(BUILD)/media_sources_gen.mk
+MEDIA_SOURCES := $(shell $(MEDIA_CONVERT) --list)
+MEDIA_FORCE := $(if $(strip $(filter-out $(MEDIA_SOURCES),$(MEDIA_SOURCES_GEN)) $(filter-out $(MEDIA_SOURCES_GEN),$(MEDIA_SOURCES))),media-force)
+media-force:
+.PHONY: media-force
+
+$(BUILD)/pbio_image_media.c $(BUILD)/pbio_image_media.h $(BUILD)/pb_type_image_attributes.c: $(MEDIA_CONVERT) $(MEDIA_SOURCES) $(MEDIA_FORCE)
 	$(ECHO) "Generating image media files"
-	$(Q)$(PYTHON) $(MEDIA_CONVERT) $(BUILD)
+	$(Q)$(PYTHON) $(MEDIA_CONVERT) --dest $(BUILD)
 
 $(BUILD)/font_liberationsans_regular_14.c: $(PBTOP)/lib/pbio/src/image/fonts/LiberationSans-Regular.ttf $(FONT_CONVERT)
 	$(ECHO) "GEN $@"
diff --git a/lib/pbio/src/image/media.py b/lib/pbio/src/image/media.py
index dba3fc0de..6ae291f84 100755
--- a/lib/pbio/src/image/media.py
+++ b/lib/pbio/src/image/media.py
@@ -1,38 +1,54 @@
 #!/usr/bin/env python3
 import argparse
+import sys
 from pathlib import Path
 from PIL import Image
 import cairosvg
 
 # Take build directory as argument to save generated C files and PNG files.
 parser = argparse.ArgumentParser(description="Convert image files to C structs.")
-parser.add_argument("dest", help="Destination build folder for PNG files.")
+parser.add_argument(
+    "--dest", default="build", help="Destination build folder for generated files."
+)
+parser.add_argument(
+    "--list-sources", action="store_true", help="Only list sources files."
+)
 args = parser.parse_args()
 
+media_dir = Path(__file__).parent.relative_to(Path.cwd()) / "media"
+
+# Collect all SVG and image files in media_dir (svg, png, bmp, jpg), including subfolders.
+media_images_sources = (
+    list(media_dir.rglob("*.png"))
+    + list(media_dir.rglob("*.bmp"))
+    + list(media_dir.rglob("*.jpg"))
+)
+media_svg_sources = list(media_dir.rglob("*.svg"))
+media_sources = media_images_sources + media_svg_sources
+media_sources.sort()
+
+if args.list_sources:
+    for m in media_sources:
+        print(m)
+    sys.exit(0)
+
 build_dir = Path(args.dest)
 build_dir.mkdir(parents=True, exist_ok=True)
-media_dir = Path(__file__).parent / "media"
+
+media_gen = []
 
 # Convert all SVG files in media_dir to PNG and save in build_dir if not already present.
-svg_files = media_dir.rglob("*.svg")
-for svg in svg_files:
+for svg in media_svg_sources:
     png = svg.with_suffix(".png").name
     png_path = build_dir / png
-    if png_path.exists():
+    media_gen.append(png_path)
+    if png_path.exists() and png_path.stat().st_mtime >= svg.stat().st_mtime:
         continue
     with open(svg, "rb") as svg_file:
         png_bytes = cairosvg.svg2png(file_obj=svg_file)
         with open(png_path, "wb") as out_png:
             out_png.write(png_bytes)
 
-# Collect all image files in media_dir (png, bmp, jpg) and build_dir (png), including subfolders.
-media_images = (
-    list(media_dir.rglob("*.png"))
-    + list(media_dir.rglob("*.bmp"))
-    + list(media_dir.rglob("*.jpg"))
-    + list(build_dir.rglob("*.png"))
-)
-
 
 # Convert rgba to monochrome, treating fully transparent pixels as white.
 def is_black(r, g, b, a):
@@ -60,6 +76,7 @@ def image_to_8bit_map(img):
 
 
 # Process each image.
+media_images = media_images_sources + media_gen
 results = {}
 for img_path in media_images:
     with Image.open(img_path) as img:
@@ -129,3 +146,8 @@ def image_to_8bit_map(img):
     f.write(
         "MP_DEFINE_CONST_DICT(pb_type_image_attributes_dict, pb_type_image_attributes_dict_table);"
     )
+
+with open(build_dir / "media_sources_gen.mk", "w") as f:
+    f.write("MEDIA_SOURCES_GEN = \\\n    ")
+    f.write(" \\\n    ".join(str(m) for m in media_sources))
+    f.write("\n")