What causes "Warning: garbage data found in JPEG file " in DrKLO/Telegram?

Re-encode the JPEG file to normalize the stream: jpegtran -copy none corrupt.jpg > clean.jpg.

Warning: garbage data found in JPEG file

Error message

Warning: garbage data found in JPEG file

What it means

The next_marker() function in wrjpgcom scans the byte stream for JPEG markers (0xFF followed by a non-zero marker code). If it encounters non-0xFF bytes before finding a marker, it counts them as 'discarded_bytes' and warns the user. This indicates the JPEG stream contains unexpected data between markers. This is the same logic as rdjpgcom's next_marker, applied when writing comments. The function still continues processing.

Source

Thrown at TMessagesProj/jni/mozjpeg/wrjpgcom.c:200

{
  int c;
  int discarded_bytes = 0;

  /* Find 0xFF byte; count and skip any non-FFs. */
  c = read_1_byte();
  while (c != 0xFF) {
    discarded_bytes++;
    c = read_1_byte();
  }
  /* Get marker code byte, swallowing any duplicate FF bytes.  Extra FFs
   * are legal as pad bytes, so don't count them in discarded_bytes.
   */
  do {
    c = read_1_byte();
  } while (c == 0xFF);

  if (discarded_bytes != 0) {
    fprintf(stderr, "Warning: garbage data found in JPEG file\n");
  }

  return c;
}


/*
 * Read the initial marker, which should be SOI.
 * For a JFIF file, the first two bytes of the file should be literally
 * 0xFF M_SOI.  To be more general, we could use next_marker, but if the
 * input file weren't actually JPEG at all, next_marker might read the whole
 * file and then return a misleading error message...
 */

static int
first_marker(void)
{
  int c1, c2;

View on GitHub (pinned to 45ab8f4308)

Solutions

Re-encode the JPEG file to normalize the stream: jpegtran -copy none corrupt.jpg > clean.jpg.
Obtain the file from a trusted source to eliminate corruption.
Inspect the file with a JPEG analysis tool to identify the garbage region.
If the file still works correctly after wrjpgcom processing, suppress stderr in automated pipelines.

Example fix

# Normalize the JPEG stream before adding comments
jpegtran -copy none input.jpg > cleaned.jpg
wrjpgcom -c "My comment" cleaned.jpg > output.jpg

Defensive patterns

Strategy: validation

Validate before calling

# Validate JPEG stream integrity before writing comments
if ! jpegtran -copy none "$input" > /dev/null 2>&1; then
  echo "Warning: $input has structural issues" >&2
fi
wrjpgcom -c "comment" "$input" > output.jpg

Prevention

Pre-process JPEG files through jpegtran to normalize the stream before wrjpgcom.
Validate JPEG files with a decoder before passing them to wrjpgcom.
Redirect stderr in automated pipelines if the warning is non-fatal and the output is correct.

When it happens

Trigger: Feeding a corrupted or non-standard JPEG file to wrjpgcom; a JPEG file with stray bytes between marker segments; a file with embedded non-JPEG data that the parser must skip over; a file that has been improperly edited or concatenated.

Common situations: Processing JPEG files from untrusted sources; files with APP markers containing malformed data; JPEG files that were edited with non-compliant tools; files recovered from corrupted storage; files with embedded thumbnails that have incorrect segment lengths.

Related errors

AI-assisted analysis of DrKLO/Telegram@45ab8f4308 (2026-08-14). Data as JSON: /api/errors/4e5f035fccf098c0. Report an issue: GitHub.