You can use FancyAudio gem for this. It can add album art to mp3 files. Documentation is available herehere.
features
- add album art to single mp3 file
- add album art to multiple mp3 files.
Below screen shot shows the output of fancy_audio when run in a folder containing an image and multiple mp3 files
Below screen shot shows the output of fancy_audio when run in a folder containing mp3 and image files

