A common problem users have is that there file type is being 'denied' by the system. The design system prefers jpg files - important - make sure the file extension name is ".jpg" in lower case not ".JPG" or “JPEG”. To change the file type name, just right click on the file, click 'rename' in the box that pops up and change it to lower case.

We cannot accept bitmap files (.bmp) or pdf files (.pdf). You can change your file to a jpg by saving it as one.