[SansMerci]

(Image now taken down for privacy).

I've seen this orange/green effect used in a hell of a lot of pictures now. Is this effect built in to a certain program? I'm assuming it is, purely because of the number of times I've seen it used?

[najinaji]

It can be done using an image-editing software, but sometimes a film camera like the Diana is used and it naturally gives that effect.

[imy7]

A lot of people have iphone apps that do all the same effects so that could be something you're noticing.
This doesn't look like an iphone image though, so the next thing i'd say is that its been done on photoshop. but you said you've seen it used loads, and most people aren't particularly skilled at photoshop sooooo i'm not really sure! if it was done in photoshop it looks like they've added a navy layer set to exclusion, then added a high opacity orange photo filter :P

[DanBrwn]

So there is no preset for doing this effect but I know what it is and what you mean. Mainly because ever second person on the internet asks about it. Its called Tone Splitting and you do it by adjusting the tone curve of the image