In most scenarios, cpt to jpeg conversion is an attempt to convert Corel Photo-Paint pictures (.cpt) to JPEG format. It appears that .cpt images can be simply re-saved as .jpeg or .jpg files in Corel PhotoPaint itself, or some graphics editor or convertor that supports CPT format.
Old program for Windows Mobile called Pocket Slides used .cpt files for presentations and these could have also been exported as JPEG images with the app, but that's something very old.