Have you tried editing their photo? I know you can assign your own photo to each contact, but I think there’s also an option to delete the photo altogether. The downside to this is you have to do it for each contact individually. Go to Contacts > select the contact > click “change/assign image” (or whatever lingo it uses) > select “delete image.” I think that removed the image completely. What I don’t know is if it shows no image at all or if it shows the standard grey outline of a person as their image. Anyway, hope this helps, if not, well, it was worth a shot.