Where is the photo stored? If it is on a CD, likely you can't delete
it. If it is a folder to which you do not have delete rights, you can't
delete it.
Remember the files are not stored in Photomanager. Just like Word, the
files are stored elsewhere.
I don't know Photomanager, but I would guess it does store thumbnail
images to display quickly. You may be able to clear those out or not. I
guess you may need to hunt around the menus. Is Photomanager a Microsoft
product?? Part of an office program?