'pm me and I'll show you the picture'
Then just never reply. Or reply with something like 'I can't be arsed to find it right now. I'll get it later.' Or just use BoB's description. I think it would be funnier if we only give them bits and pieces and let them speculate, though. 'It was a picture involving tentacles. That's all I'm going to say', 'It had a young girl in it, and I'm quite sure what she was doing was unbecoming for someone of her age', 'It depicted an act illegal in 43 states', etc.
BoB, I agree that your option 1 would be more believable. The only problem is that 3 of those four members are either currently inactive, or just got back from a long period of inactivity. It doesn't seem like that would have as much of an impact as someone as post happy as myself or Yams stepping down.
With option 2 I could quit because you guys removed Feedback, a forum I love to spam in. Yams would be last and he could name any number of reasons: 'No fun without Del', 'I agree with Unne/Leeza', 'Too much drama', etc.