some photos in my iPhoto show exclamation point

After using a software that deletes duplicate pictures, now when I go into iphoto, some of my photos show an image of exclamation point inside a triangle. When it is small, it shows the thumbnail of what its supposed to be, and also when I click on it to make it bigger, it shows the actual picture for a split second and then becomes an exclamation point. Is there any way I can retreive the picture? (it must be somewhere because it shows the actual picture for a split second)