Can this iMac be upgraded?

Hi, i'm new to the forum so please forgive me for posting in the wrong section or inappropriate questions!
I have a MACBook Pro, iPads and iPhones at the moment.
Son in law has the following 'old' iMac.
How can we find out what the latest OS is that can be loaded?
I do a lot of photography and video using a HD Pro, can this be upgraded to a decent spec to run photo/video editing software?
If he decides to sell it, how can we find out how much it is worth?

(I may have raised this in an incorrect section, if so can a Mod move it please?)

To answer the very absolute question of "can it be upgraded?" the answer is yes. You can add RAM up to 4-6GB, and probably more/faster storage. It can also run the current Mac OS, 10.11 "El Capitan."

However, it's still a Core 2 Duo, which is about eight years old. A Core 2 Duo it will stay. It will be sluggish doing modern, intense tasks. It also won't likely take the next version of OS X.

Since this forum is global, how much it's worth is totally up to your local economy. Basing on the Big Mac Index, probably about 30-40 Big Macs.

Thanks for the reply s.subzero.
I use Lightroom so chances are its not worth wasting money up grading it, only to find its sluggish and freezes all the time.
Think i'll advise him to stick it on eBay, seems the going rate is around the £150, so you 30-40 big macs wasn't too far out