What is the Depth parameter?
Many new users of DevIL think that the Depth parameter is pixel depth (ie. bpp), but it is really the image's depth. DevIL supports image volumes (3d images), and these can just be thought of as 2d images overlaid on each other. Normally, you should use 1 as the Depth parameter.
What is the Bpp parameter?
Bpp is simply bytes per pixel. Do not confuse this with bits per pixel. DevIL never asks for bits per pixel as a parameter.
Images loaded flipped
When loading images DevIL preserve their origin. If you want them at a fixed origin you must enable IL_ORIGIN_SET and set the origin you want.