I don't know if this will help anyone when determining whether to put photos of their family's children on places like Gransnet or Facebook, but here is the Copine deifinition of the lowest level of interest (level 1) that abusers who look for images will show interest in. Copine is the project developed by Professor Ethel Quayle at Cork University, together with the police and probation service, to define 6 levels of seriousness to aid prosecution regarding abusive images. These levels are used by judges. There's more information on Google:
Level One. Non-erotic and non-sexualised pictures showing children in their underwear, swimming costumes, etc. from either commercial sources or family albums; pictures of children playing in normal settings, in which the context or organisation of pictures by the collector indicates inappropriateness.
As you can see, it is anything that hints at their view of inappropriateness - underwear, swimming costumes. Clothed children hold no interest, except for rare cases where the offender knows the child and would have a collection of photos to build up with other photos.