Re: What kind of digital post processing is used here?
It just looks like a partial sepia tone, I would have to see the original to know for sure.
What I would so is take your base image (layer 1) and duplicate it (layer 2)
With Layer 2 selected convert it to Sepia Tone (read this tutorial if you are unsure how to do that):
http://www.easyelements.com/photoshop-sepia-tone.html
** There are many other techniques to create Sepia tone, some featured on DEVPPL, but I find this way to be easiest.
Then set Layer 2's opacity to between 65 - 75%.
I am sure it isn't perfect, but without seeing the base image it is really challenging to see what affects were applied.
Good Luck!