If your image files aren't recognised by RapidStudio they are probably the wrong format.
As photos RapidStudio will recognise RGB JPG files.
As cliparts, you can use RGB JPG files BMP files or 32bit PNG files.
RapidStudio will warn you if your photos are low resolution, if they are in their native resolution.
If the resolution of the image has been increased, the resolution calculator in the software will not provide accurate information.