I have tried to add a snapshot from PC to tread many times. I have always failed. I do it now from Photobucket which is very easy. I expect there is a way of doing it,I am sure someone here will advise you.
To the best of my knowledge, You need to use photobucket or a similar program.
I dont know away of adding a photo direct from the PC. I know thereare a few PC pro's on here Barry D and Big giraffe spring to mind no sdoubt they will share their wisdom if we are missing a trick
Channa