1. Open an image of any size preferably of lots of colors. Duplicate the image layer (Layer > Duplicate Layer) and select the duplicate layer.
2. Using Pen tool select a portion of hair and paste it on new layer and name it, say, hair.
Click on layer named hair. Now we are going to make cracks that will make up the mosaic. Add a shadow to this layer. Layer > Layer style > Drop Shadow.
I have used these settings.
After this go to Layer > Layer style > Bevel and Emboss and Use these settings
Select the Eraser tool and choose a 3 pixel round brush and delete in a tile-shaped pattern. (regular or irregular polygon shape. I prefer irregular polygon for the true mosaic effect). Now the picture should look some what like this.
Follow the similar procedure for the rest of the hair strands
Now merge all the hair strands layers.
For this first we have to hide image layer.
To hide a layer, click once on the eye icon. The eye will disappear and the layer will become invisible.
To show the layer again, click again on the eye icon. The layer will reappear
After hiding merge the layers.
Layer > Merge down.
Now coming to dress we should pay attention to the picture and find out the appropriate selections on the dress layer. In the particular picture I let the curves/frills/folds (whatever you call it) of the dress be a guide to how the tiles should be shaped.
Go ahead and apply the same procedure to her whole body including face.
Now merge all layers (hair, dress, body, face)
Layer > Merge Visible.
This effect works out for the image where you need to take care of many details of the image like eyes, nails of a finger, hair (I hope you got the idea).
Using clone stamp tool I changed the background.You don't see the wings now ;-)
But for the image which broad strokes of Mosaic effect are enough the steps involved to achieve that effect is almost totally different from the ones I listed above.
So to do that go for an image that normally is used as a background to the principal image (like above). I chose this and here are the steps.
Open the image and duplicate the image layer.
Now, create a brand new layer and fill it with dark green color and let’s call that layer color.
Place this color layer in between the original image layer and its duplicate.
Add Noise to this color layer.
Filter > Noise > Add Noise and use the below settings.
Create a new document of size 1200 X 1200 pixels.
Fill it with black color.
Create a new layer and call it shape.
Select whatever tool you like and draw irregular shapes and fill it with white.
It should look something like this.
Drag this shape layer on to image copy layer created in step 1
Now select all the irregular shapes you created in the previous step. Easy way to do it is by clicking on the shapes layer while holding the Ctrl key. Invert the selection. To do this, either open Select menu and click Inverse or press Shift, Ctrl and I keys simultaneously. Now click on your duplicate image layer created in the step 1. Now we can delete our selection by hitting Delete key in the keyboard. As a next step hide the shape layer. Picture should like this once you’re done deleting and hiding.
For the mosaic effect, go to Layer->Layer Style->Inner Shadow and use these settings.
Now go to Layer->Layer Style->Bevel and Emboss and use these settings
Here is what we have after applying those settings.
5. To consummate our little Mosaic Effect exercise let’s combine both the pictures we photoshopped.
Do the final touches to hair and lips.
By using clone stamp tool we can fix hair.
Add a little color to the lips.
Merge the layers.
Layer > Merge down
Here's the final picture.