My girlfriend bought an HP All-In-One (non-touch screen) for her son for Christmas 2014 - Per the HP Web site it was warranty registered 12/24/14 (when he powered it on and set it up)
This year for Christmas we bought him a nice "Gaming Keyboard" - he went to plug it in & ALL the USB ports on the All-In-One went dead (and without a touch screen that is the ONLY way you get input to the device)
We called HP on 12-26-15 and they told her "It's a software problem not hardware & even if it was hardware it's out of warranty" - 1 Year warranty - out by 2 days.
And since all the mouse / keyboard inputs are USB and the USB isn't working - how exactly do they propose we fix a "Software Problem" ??
Side note - the system powers up & boots fine then just sits there waiting for you to log in w/ no input devices.
It is now currently gathering dust in my workshop floor because I can't find parts for it anywhere and I can't find anyone else that wants to try and work on it (presumably for the same reason - no parts).
I have worked in the IT field for over 22 years, have dabbled with building & programming for 8 or more years before that, and I have built computers from scratch back when a "DX" processor was a hot ticket and the Motherboard "Beep" speaker was the only sound you got and I can say one thing with absolute certainty - until ALL personal computers are All-In-One devices; I'll never own one.
As always - Your mileage may vary.
My recommendation is get a nice monitor and cheapest desktop that will run the photo editing software you want to use (read their required & recommended hardware specs). By the time the software requirements exceed what the computer will deliver, you would be better of with a new computer rather than upgrading that one.
In other words don't by a $600 computer expecting it to last 3-4 years when a $300 system will work now; Buy the $300 one & in 2 years buy another newer $300 one.
I will also echo what KennyG said about multi monitor systems. Right now at work I'm running the Laptop screen and 3 17" Wide Screen monitors (one of which is thru a splitter that's also attached to a 46" TV on my wall)