To demonstrate the issue, this is my avatar https://xenforo.com/community/data/avatars/m/1/1110.jpg Open the image in your browser (I'm using Chrome, windows). 1. Drag the image to your desktop -> you'll get a png image rather than a jpg. If you'll right-click to <Save image as..> it will save as jpg. 2. Right-click to <Save image as..> to get the jpg image. Try to upload it as an attachment to your post, you'll get an error "The contents of the uploaded image do not match the file's extension."