all cd software will permit muli sessions for data be they Photos or something else. The problem arises when you want to create a slideshow. Various programs have number limitations for the pictures to be included. Once the slideshow is created, then that is it. But then CD-R disks are cheap.
I am not sure what the limit is for EZCD, but ON DVD by Dazzle allows up to 200 photos per slideshow. According to there manual, anyway.