This tutorial is mostly for advanced users, as it will require a lot of “manual labor”, brightening small areas in the face, adding hair from another picture, etc. If all these steps won’t be done neat, you are risking to make a funny monster, rather than a mermaid… anyway, this is what we will do:

Turn a Brunette Girl Into a Beautiful Mermaid - PS Tutorials Lorelei Web Design

Unfortunately a PSD file of this tutorial is not available at this time but as soon as we release the PSD membership club, I hope to include a file with this effect as well. Star of by taking a photo of a brunette girl. We used a downsized wallpaper of this woman:
http://vetton.ru/models/6406.html

Duplicate the photo so that you will have 2, or even 3 layers. If anything goes wrong, you can always pull out an intact layer and you can start allover again.

Select the upper layer and go to Filter >> Distort >> Diffuse Glow.
This will give your photo a nice dreamy effect for a start.

Turn a Brunette Girl Into a Beautiful Mermaid - PS Tutorials Lorelei Web Design

Next step is to colorize your photo. As you know, mermaids tent to have blueish face (they have drown, don’t forget! ) and greenish blond hair.
So, press Ctrl + U to colorize your photo (entirely) and apply these settings:

Turn a Brunette Girl Into a Beautiful Mermaid - PS Tutorials Lorelei Web Design

This is what you got. Mildly glowing and blue colored face. if you don’t wish to go ahead with your Photoshop skills and create a mermaid, you can stop here, this result may look good if you want to add mystery to your ordinary shot.

Turn a Brunette Girl Into a Beautiful Mermaid - PS Tutorials Lorelei Web Design

Next, select the Dodge Tool in Photoshop, about 3px with a soft edge, and go over the inside of the eye, lightening the eye balls and the eyes themselves, but try not to touch the contour of the eye, in order not to make the entire area too pale.