Importing photos from computer

Can anyone help? This is my first time making an animation. I want to make an animation using previously taken photos that I have saved in a folder in my computer. All the photos are JPGs in RGB, same resolution, size etc. I have amended them slightly in Photoshop to make sure they line up with each other, but I made sure I saved them all in the same format. However when I try to import them either straight into iStopmotion, or into iPhoto first, the programs only recognize the file format of 1 of my photos. I can’t understand what the issue is because they have all been saved in the same format. Please help…!