Corel Photo-Paint image
Corel Photo-Paint image (CPT) is the native format of the Corel Photo-Paint program, though this program also supports some other, more widely-used formats. It is apparently a different program from Ability Office PhotoPaint, though they both seem to be intended as replacements for Adobe Photoshop, and support the PSD format among others.
The CPT format is a multi-layer bitmap with additional information stored. There are several versions, with considerable differences. An online document referred to as "CPT file format specification" is not to be an official spec (it contains comment "Zajebiście tajemnicze pole :-P" which translates from Polish as "Awesomly mysterious field :-P"), but rather an attempt to describe the format (most likely by reverse-engineering), and is incomplete (with lots of "TODO" notes).
It usually (always?) contains a thumbnail. Both image and thumbnail are compressed.