Does your browser show image URLs when mousing over? Turn that off, because it looks like a diagram's URL encodes the entire diagram definition. Here's the URL of a random diagram:

I uploaded this to Imgur (thanks sol.ch), but is there a more direct way to post an image?

I'm using Opera, and I don't have any idea how to turn off image urls.

Does the server side script even cache the generated images?

I'm using Opera too, but I'm not seeing it--but if I remember correctly, I've used versions of Opera that will use the image URL as the alt text if no alt text is specified. That means that this problem could be fixed by just adding some short alt text for the image (like "Go Diagram"), I'm guessing.

I'm wasn't seeing the behavior before, either, but I added the alt text like you suggested for now.

Doesn't seem to have done the trick, but thanks for the effort.

It looks like your browser shows the URL regardless of the ALT text, then. I'm thinking that we're going to have to save the images on the server to adjust this, rather than generating them dynamically. I don't see how using an MD5 for a dynamically generated filename would allow for us to get around saving the images to disk since MD5 can have collisions. Perhaps we could save the files to the server using an MD5 hash for the filename, and if a duplicate filename existed, we could increment the filecount (eg. <md5-hash>1.gif, <md5-hash>2.gif, etc.). This would be inefficient for the cases where you have two of the same images (because we would generate separate, but identical images).

On the other hand, perhaps the chances of having an MD5 collision are low enough that we could use this filenaming scheme.

Also, I know Adrian wrote the wordpress plugin creating the diagram codes that did the above. Simply did an md5 hash of what was sent in to create a filename that could be checked so we didn't create duplicate images.

The chances of an MD5 collision are relatively low and I would think we wouldn't really need to worry about this. See: http://www.miketaylor.org.uk/tech/law.html for a simplified description of this. And if a collision ever did occur, I don't think we'd have to wait long to hear about it! Plenty of us follow all the Malkovich games as it is, and that's where the vast majority of the diagram images are used.

Also, I know Adrian wrote the wordpress plugin creating the diagram codes that did the above. Simply did an md5 hash of what was sent in to create a filename that could be checked so we didn't create duplicate images.

Personally, I don't really buy the argument about using MD5 without any worries at all. There have been enough exploitations of MD5 to create a concern when you're using it for an important application. A popular example is this one: http://www.win.tue.nl/hashclash/rogue-ca/. However, it is true that these people were actively trying to break the system. It's also against my philosophy to develop something with a known problem if it can be avoided (like in this case by not generating filenames at all)...

But you guys are right: there is a problem with the current implementation if the characters in the URL get too long. Also as has been said, if a collision did occur, we could address it at that time. And the probability of a collision is still low, especially if nobody is trying to attack the system. Another point is that it seems that diagrams have already been implemented in this manner without problems, so it might be OK to follow suit...

It's not as straightforward as copying what Adrian has done verbatim because of the limitations in the BBCode, but we should probably go this route. I think that the possibility of MD5 collisions is low enough that it is a much lesser issue to worry about than passing things through the URL like this.

So if we do go that route, what about using php's sha1 function? It's unlikely that we'll have an MD5 collision, and probably even more unlikely that we'll have a sha1 collision. It probably doesn't make a difference, since we'll probably get no collisions at all, but it might make me feel a little happier inside.

I'm flattered that you remembered the details of that code from so long ago