Most cameras will only view images stored within a set folder structure. If you have saved the images to new folders we suggest moving the images back to within the camera’s folder structure and you should be able to view them if in the correct format, but this may not be the case always as some cameras will only display images with the correct EXIF information. (This is extra data stored with the image).
If you have modified the original image or changed the file format using Adobe Photoshop or similar the image may now not be compatible with your camera’s operating system and so will not display on the camera’s viewing screen (the images will be perfectly safe and fine to print).
To avoid problems it is best not to save changed images back to the memory card if possible.