When I put a photo in the backpack and I disconect from the server the photo is black.

Is this normal? if so it would make sense to put it on the blacklist automatically.

Yes, this is normal since Backpacks use custom item persistence which doesn't have a way to track photos yet. It also might be challenging to track them across wipes for the folks who have that enabled. Thanks for the suggestion about automatically blacklisting.

Marking this as solved since it was addressed in v3.7.0. Keep in mind that the photograph will become black again after wipe, if the plugin is configured to persist backpacks across wipes. Further improvements can be made to persist photograph data (and other entity data) across wipes in the future.