I'm ignorant to snapchat (by choice or just...plain..ignorance) so I googled and it says "Users set a time limit for how long recipients can view their Snaps (as of April 2014, the range is from 1 to 10 seconds),
[6] after which they will be hidden from the recipient's device and deleted from Snapchat's servers. "
Does this mean images can be sent and never have the ability to be tracked? If so, their mention of a breast image is either what the boy told them or he quickly saved it to his device, which I'm sure a screenshot could do.