Description#

A JPEG image file that appears to be corrupted and cannot be opened.

Analysis#

Examining the file header reveals the corruption:

$ xxd sigmatour-image.jpg | head -3
00000000: ff00 0000 0000 0000 4946 0001 0100 0001  ........IF......
00000010: 0001 0000 ffdb 0043 0002 0101 0101 0102  .......C........
00000020: 0101 0102 0202 0202 0403 0101 0102 0504  ................

The file starts with FF 00 00 00 00 00 00 00 but a valid JPEG/JFIF file should start with:

• FF D8 - JPEG SOI (Start of Image) marker
• FF E0 - APP0 marker (JFIF)
• 00 10 - Length of APP0 segment (16 bytes)
• 4A 46 49 46 - “JFIF” identifier

Notice that 49 46 (“IF” from “JFIF”) is still present at offset 8, confirming this is a corrupted JFIF header.

Solution#

Restore the correct JPEG/JFIF file signature:

# Method 1: Using printf and dd
$ cp sigmatour-image.jpg fixed.jpg
$ printf '\xff\xd8\xff\xe0\x00\x10\x4a\x46' | dd of=fixed.jpg bs=1 count=8 conv=notrunc

# Method 2: Using Python
$ python3 -c "
with open('sigmatour-image.jpg', 'rb') as f:
    data = bytearray(f.read())

# Fix JFIF header (bytes 0-7)
data[0:8] = b'\xff\xd8\xff\xe0\x00\x10\x4a\x46'

with open('fixed.jpg', 'wb') as f:
    f.write(data)
"

# Verify the fix
$ file fixed.jpg
fixed.jpg: JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, baseline, precision 8, 2848x1600, components 3

After fixing the header, open the image - the flag is displayed visually within the image itself.

File Signature Reference#