Here is a quite nice JPEG decoder SW running on Arduino. what could be nice is to actually cache not the full image in SRAM but the smallest decodable sub image. For Jpeg that would mean macroblocks, which are 16x16 pixels. If the caching mecanism in littleLgv could work on those macroblocks, eachtime a region on the screen gets dirty ( button overlap), to get the pixel data, only that macroblock(s) would need to be decoded.
@kisvegabor does this makes sense regarding the way littlelvg works and manages the data?