How can you find out where a picture was taking by looking at the coding in the file?

I read a story about some Burger King employees who screwed around with customers by stomping on some salad without them knowing. One of the employees took a picture of it on their phone and posted it on the Internet. Some hackers (not really, but for lack of better term, just people who knew what they could do) apparently were able to find the Burger King that this was done by downloading the picture and somehow, within the code, finding out where it was taken.

I wonder how that’s possible. Like can anyone really check up on that without necessarily taking a lot of computer courses or is it much harder to do? And does this mean that ANY picture you get online you can figure out where it was taken, or would this only work for cellphone pictures?