You can upload photos so long as you keep the filesize less than 100kb.
You will need to have a graphic editing software (search the forums for recommendations of a few free ones) to reduce the size of your image. Most editors these days display the approximate final size and you can tweak the quality settings to have the best quality and yet not exceed the limit.
On Windows, you can right-click on a file and click on Properties to view file details, including filesize. If your Explorer status bar is visible, the size will be displayed there when you select the file.