I want to know how many times the same image was added to the ListBox of images

If you want to check that the image itself, regardless of the file name, is not duplicated, then create an MD5 checksum for the image data and save that.

If you want to make sure both of them are always linked, either mark it at the end of the file, or create a class that contains the image and the checksum together.

MD5 validation can be used to distinguish between any data file, even different versions of the same file, if the content is different anyway.