You can shop someone else into the photos in Kevak's place, then distribute them like that.
This reminds me: I don't think any photos were taken of our 'Melbourne Bay12 Lasertag-Meetup-Extravaganza' back in the day. Aw. Glad to hear you guys had fun and didn't die breaching a volcano or something!
If you know how, it's easy to undo a photoshop.
(Note: not intending to photoshop you, just trying to clarify as someone who knows how to photoshop.)
Only if non-destructive editing has taken place. And even if that editing is applied by placing a layer over the main one, it becomes destructive once the image is flattened upon export. The only thing that would easily be undone would be some kind of substitution, like playing with the color balance. Anything else would require the PSD from which the shopped image was exported. Simply swapping faces and such would leave too much of the original person's image intact, but entirely removing or covering (effectively the same as removing) leaves nothing with which to reconstruct. Of course, entirely replacing someone in a photo either requires having a picture of the replacement in the right pose to entirely cover the original person, or a reference photo of the background with which to replicate the part their image covers.
However, since iirc you were standing to one side, it would be much simpler to just crop you out of the photo. Which can even be done with the default image viewer in Windows, and cannot be undone. But I don't really want my image passed around either, unless I'm the one passing them around.