To address these things in no particular order:

We support
.jpg
.png
.gif
.bmp

When you attach a picture to a post, it will bring up a grid of the allowed file types and thier max dimensinos and filesize. bmp's are purposely clamped down to encourage folks to use the other more effiecient formats, but is still there for that odd poster with a smallish image and no image software.

The posting rules are in the terms and conditions link at the bottom of the forum.

There are thumbnails handled by the system, but they still need some configuration tuning.