Software released at Comiket 83 containing official K-On! art covering the two seasons and movie, both versions of pre-existing works and newly released art. The images (423 different artworks) are stored in the data files as encrypted JPEGs in five different resolutions, and are not too hard to datamine .

There is a Yande.re equivalent, but the images there are likely doubly lossily compressed (after comparing file sizes and artifacting with the properly extracted ones).

(NB: I plan to upload these over time, as and when I have time to tag etc. - user #1297069 (fn0))