How can I "colorize," a photo in a style similar to this?

[AntiqueFlaneur]

How can I colorize a photo in a manner similar to this?

Originally that was just a picture of a marble statue. How would you go about adding the design?

[carl123]

Find a pattern you like on the internet. Clip the pattern to the statue. Change blend mode of pattern to whatever you like best 

Or you can search the Resources forum for free styles people have uploaded that may do what you want

 

[DWright]

You can also use a Mask with Opacity and Blend mode adjustments to replicate this effect

 

[Andy05]

In addition to the two examples above, I'd start with some different approach. With this method, the original shapes, lines and shadows are maintained. Here's a (very!) quickly done low-res example. But with some fine-tuning it should provide the wanted results.

These are the steps used (every step gets added as a layer above the previous one, all of them applied to the masked object):

• duplicate the image
• mask the object
• desaturate the masked object (I used HSL, but B/W would work as well, maybe even better, depending on the motive)
• add a curve like shown in my example, go wild with the nodes!
• Add a gradient map (here's where you pick your colours, the more "rainbow-ish", the better).
• In this case, I added a gaussian blur (was needed due to low res source)
• set the masked object's blend mode to a setting, which will blend the colours to the original underneath (e. g. overlay)