Improper image type is likely to mean that it is saved as the wrong file type.

The file has to be saved as a jpg png or gif. - the file name would end up being nameoffile.png or nameoffile.jpg

This is in addition to the 100x100 pixel limitation if it is to be uploaded to the site and used.

As Richard highlights you can host an image on another picture hosting site and use a link but this is probably more complex.
I have a file saved to the partner site tm-img and use this to provide my avatar.


Modern software will often save as more complex file types some of which can be found here if you want to check them - https://en.wikipedia.org/wiki/Image_file_format

If you have an image in the wrong format then the easiest way of migrating it to be used is to open it in a picture editing application and try and do a "save as" then look if there is a jpg etc.

Everyone loves a Morgan. Even me, unless it's broken again.