diff --git a/packages/markitdown/src/markitdown/converters/_markdownify.py b/packages/markitdown/src/markitdown/converters/_markdownify.py
index 3811ae3c9d..0e9fd3bf49 100644
--- a/packages/markitdown/src/markitdown/converters/_markdownify.py
+++ b/packages/markitdown/src/markitdown/converters/_markdownify.py
@@ -127,7 +127,7 @@ def convert_img(
             return alt
 
         # Remove dataURIs
-        if src.startswith("data:") and not self.options["keep_data_uris"]:
+        if src[:5].lower() == "data:" and not self.options["keep_data_uris"]:
             src = src.split(",")[0] + "..."
 
         return "![%s](%s%s)" % (alt, src, title_part)
diff --git a/packages/markitdown/tests/test_module_misc.py b/packages/markitdown/tests/test_module_misc.py
index 7001b42b95..a8f4d744fd 100644
--- a/packages/markitdown/tests/test_module_misc.py
+++ b/packages/markitdown/tests/test_module_misc.py
@@ -227,6 +227,21 @@ def test_data_uris() -> None:
     assert data == b"Hello, World!"
 
 
+def test_uppercase_data_image_uri_is_truncated_by_default() -> None:
+    markitdown = MarkItDown()
+    html = b'<html><body><img alt="dot" src="DATA:image/png;base64,AAAA"></body></html>'
+    stream_info = StreamInfo(mimetype="text/html", extension=".html")
+
+    result = markitdown.convert_stream(io.BytesIO(html), stream_info=stream_info)
+    assert result.markdown == "![dot](DATA:image/png;base64...)"
+    assert "AAAA" not in result.markdown
+
+    result = markitdown.convert_stream(
+        io.BytesIO(html), stream_info=stream_info, keep_data_uris=True
+    )
+    assert result.markdown == "![dot](DATA:image/png;base64,AAAA)"
+
+
 def test_file_uris() -> None:
     # Test file URI with an empty host
     file_uri = "file:///path/to/file.txt"