It might be different for you ... I'm on a Samsung tablet, but I press upload file and just browse for the location....it gives me three options, Camcorder, Camera and File....just click file and it's there, just need to select thumbnail or full image.
If you’re using a tablet or mobile you’ll need to use the ‘upload a file’ option and have the image saved in your photo library.
You can just copy and paste it which is the easiest way. Failing that, click upload a file and then browse your computer/phone to find where you saved it.