I'm trying to add a large avatar to my homebrew item but whenever I click to save the change I get a server error. This does not happen with any other changes I have made to the item.

Either the image is too large or it is an unsupported file type.

I have tried several image sizes and two different file types (jpeg/png). I still get the same result.

Sidenote: A few days ago (while editing a previous version of this same item) I uploaded a jpg image and it worked fine. I tried again today with the same image and received the error. 

I dunno then. .jpeg should work, as should .jpg, but I don’t think a .png will work at all. Are you trying to add both pics and save them both at the same time? That doesn’t work, you have to add a pic and save the homebrew, and then add the other one and save it again.

I can tell you that the only people who can see those images are you and people in DDB campaigns with you. Once you publish a homebrew, the images get hidden from the public in case they are either inappropriate, or copyrighted materials owned by someone else.

I got around this by adding the images separately. Save the large one first, then go back to edit it and add the small image. This is with a .png file.