-i DIR, --write-images=DIR
Causes all attached images (APIC frames) to be written to the specified directory. They are named by their "image type". For example, if the image is a png and the type is OTHER, a file named OTHER.png is written to the desired directory. If the file name already exist, a unique numeric value is appended to the type string.

Man online - eyeD3 (1)

$ eyeD3 -i ./ hoge.mp3

でカレントディレクトリに画像が書き出される。アルバムアートに余白があってImageMagickでtrimキメたい時などに便利。