There are many reasons why you cannot upload images into MyPhotoApp. In most cases, MyPhotoApp will provide an appropriate error message for you.
But in some cases, it does not. The simplest thing to do is refresh your browser by holding down the shift key and clicking the page reload icon in your browser and try again and see if that will resolve your photo upload issue.
If not, you can see if any internal error messages are being displayed. You can do that by using the chrome browser. Bring up MyPhotoApp, and then try and upload your image. If it still fails, on the chrome tool bar, click on View -> Developer -> Javascript Console. This will open a window on the right hand side on the screen. If there are error messages there in red, please copy and past them into a support ticket.