You will be required to submit a photo of yourself for your application. This should be a clear head shot of yourself that is under 5MB in a JPEG format. You will not be able to submit a photo that is larger than 5MB.
You can resize photos by using a photo program on your computer, such as Paint (PC) or Preview (Mac). Alternately, you can try the following website, which allows you to upload the image, resize it and then download it in multiple formats: http://www.resizeyourimage.com/