Images must be given a unique page title. The page title must end with the same extension that your image ends with (e.g. .jpg or .gif).
You need to give every image a very unique title so someone else doesn't inadvertantly over-write your image by saving another image with the same title. You can create unique image titles by including the names of the individuals referenced in the image along with relevant dates, places, and/or document type in the title. For example, if your image filename is grandpa.jpg, then your image page title could be something like Elmer Hathaway birth certificate 18 May 1851.jpg. Another possibility is to include the full title of the person or family page including the index number in the image title. For example, Elmer Hathaway (1) birth certificate.jpg. It's up to you.