Thanks for taking the time to put these together, but there are a few issues:
1) Everything should be lowercase for linux compatibility (Your directory name is "Mapshots", not "mapshots").
2) The screenshots are way too large. Not only does this make the download large, but it takes up a ton of memory when you're displaying them in-game.
3) All textures should have dimensions that are powers of 2.
4) Mapshots should use screenshots taken with a 4:3 ratio (ex: 640x480 or 800x600).
5) Looks like you have your brightness settings jacked up quite a bit - you should probably take the screenshots with the standard settings.
Standard size for mapshots is 128x128.