I have a lot of mp3 files which I get from Game/Anime OSTs, ED/OP Singles and the Collector's Soundtracks that come with Premium or Limited Edition Games. A lot of the time these aren't tagged with their album name, track name and artist (with the exception of some like Disgaea 4, Puela Magi Madoka Magika).
Now I sync all these files to my old iPhone 4 which I now use as my music player (because I have an iPhone 5 and my iPod Touch only has 8GB compared to my iPhone 4 which has 32GB). My computer on which I store all my music, work and games does not connect to the internet, so it's kind of a pain to download .txt files with track information and use Windows to change it manually.
I figure the quickest way to do it is to add album art to all the files and have them grouped correctly in iTunes. While I can do the grouping just fine, I can't add the album art.
I am wondering what program can I use to add album art to mp3 files which would make them still work in iTunes (because if it works in iTunes, it will work for any Apple product I sync it to).