When uploading a headshot image to a user profile, any size can be used. The image will be scaled to 200 x 250px size when used on the profile page, or proportionately if it is a different ratio. On the gallery view the image is scaled to 100px wide - there is no height restriction in the scaling on this view.
The image should be a standard .jpeg, in rgb mode, or a .png - preferably with a resolution of 72dpm. Images in other formats could be uploaded and the image would be visible on the editors view of the profile page but not in the web view of the saved page.