Found a cool blog from a guy called Jon Sangster. It had a page about Red Dead Redemption 2 - long for rdr2. What a magnificent find! It explained why the in-game photos cannot be opened by most image viewing apps, and how we can actually “extract” the photos from the files produced by the game.

Here goes the ruby code from Jon:

NOTE! Disclaimer, this code is not mine, it is from Job Sangster, the blog I reference above. His GitHub looks very interesting also. If you are interested about software made in C and Ruby, I recommend viewing his repositories. They look interesting :).

# Convert Red Dead Redemption 2 Photos to JPEG.
# Usage: ruby convert.rb < PRDR3834231157 > photo.jpg

prev_byte = 0x00
in_jpg = false

$stdin.each_byte do |byte|
  if in_jpg
    print byte.chr
    exit if byte == 0xD9 && prev_byte == 0xFF
  elsif byte == 0xD8 && prev_byte == 0xFF
    print "\xFF\xD8"
    in_jpg = true
  end
  prev_byte = byte
end