Bitmaps in DB are like seperate screens that the user cannot see.
Images are fixed storage areas for bitmaps.
For example, you could build a Hud or map for your game using a DB bitmap, by pasting 'images' as tiles at various positions on the bitmap. you can also cut and paste specific sections of a bitmap to wherever you want. Think of it as an off screen workspace. The big advantage of a bitmap is that it can be any size you like. But you can only have 32 of them.
Images however, are handled as a single item. It is not possible to cut and paste specific areas of an image (with the arguable exeption of matrix textures). They are the building blocks from which other graphics are made. When you paste an image to the screen you are actually pasting it onto 'bitmap 0'. Images tend to be limited to a specific size by your graphics card, but you can have over 64000 of them loaded if you want.
Hope that makes some form of sense!
Strings are PChars ??????? What a World