Unless you have access to the original Corel PhotoPaint with which you could easily save .cpt pictures to other formats, you will have to rely on some 3rd party conversion solutions that can handle cpt to tiff conversion, for example reaConverter.
Convert Corel PHOTO-PAINT bitmap file to Aldus Tagged Image File Format (TIFF) bitmap image.
We have found one software suitable in our database for this conversion.
Microsoft Windows software - convert cpt to tiff on Windows
realConverter is a batch conversion application that supports a wide variety of mainly graphics formats.
Convert from cpt file
to tiff file
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.