On the bottom of the Task Instructions, after you press the robot check is how to submit or report a task.

If you need to send more than 1 picture as proof, I suggest you try using Photo Collage by Idealapp. It's free, easy to use and you can find it here. There's also a handy tutorial here. Alternatively, you might want to give this online tool a try here. Whichever option you choose, I hope it helps!