how do ethical pic sharing rules even work, like written out

we're heading into our first proper meet with another couple this weekend and they suggested we exchange "playtime pics" in advance just face cropped body stuff. weve never done this with anyone before. is there a script for this. like do you send first they send back, do you say "delete after viewing", do you watermark them somehow, do you only do it via certain apps. ive read about ppl getting their pics shared in group chats they never agreed to and it terrifies me... whats the actual practical etiquette ppl follow