I've got a few diagrams (on the twin paradox), that I'd like to repost occasionally. It seems that if I just post a link, people are less likely to look at them. PF, however, complains that I've already uploaded the file. I can tweak it a bit, and re-upload it, but that seems anti-social (as in trying to get around the rules), as well as being annoying to do. Finding the attach point reference from a previous post and putting that into the attachment list doesn't seem to work either, at least not the way I tried to do it. I.e. I can post a link in the forums, like https://www.physicsforums.com/attachment.php?attachmentid=37080&stc=1&d=1310342900 or even https://www.physicsforums.com/attachment.php?attachmentid=37080&stc=1&d=1310342900" But I can't attach it, at least not with that reference using "upload file from URL". Is there some trick I'm missing on how to upload something once, and have it referred to and displayed in multiple posts? Or isn't it technically possible.