I'm trying to get the file dimensions (width and height) from a jpeg (in this case an Instagram picture)
As I understand if, the width and height are defined after the 0xFF 0xC0 marker, however I cannot find this marker in this picture. Has it been stripped or is there an alternative marker I should check for?
The JPEG Start-Of-Frame (SOF) marker has 4 possible values:
If you're scanning through the bytes looking for an FFCx pattern, be aware that you may encounter one in the embedded thumbnail image (inside an FFE1 Exif marker). To properly find the SOFx of the main image, you'll need to walk the chain of JPEG markers. The 2-byte length (big-endian) follows the 2-byte marker. One last pitfall to avoid is that some JPEG encoders stick extra FF values in between the valid markers. If you encounter a FFFF where a marker should be, just increment the pointer by 1 byte and try again until you hit a valid marker.