So you need to process them a different way. Or decide if you want to accept the file or not. The whole point of checking the file type is to make sure you are getting a specific type of file. So if the image type comes across as blank, save it in a 'safe' folder and perhaps send an email to somebody to verify the image is an image before moving the file into the users account or whatever you are doing.
Or even easier, tell the end user that the file they are trying to upload does not have an image type associated with it. use a photo editor to convert/save the image as a jpg and re-upload. gimp is a free editor. There may be some online tools to convert photos as well.