Isolate Bird Head
With the eagle layer active…
Go to Properties and Remove Background.
This will result in masking out the background for you.
Soften the Neck
You need to make the neck softer to blend better. Select the Brush Tool – and set it to about size 200, and totally soft.
Make sure your colors are set to default (D), black = foreground color.
Hide the dog layer for now, then make the mask part of the head layer active…
Brush along the bottom of the neck to get something like this…
Make the Head Fit
Show the dog picture again…
CTRL+T the head layer and resize/rotate it to fit like this (you should have a bit of the eagle head sticking out the sides, covering the original dog’s head).
[Enter] to apply the transformation.
Then reduce the Brush size to about 100, and increase the Hardness to about 90%.
Brush along the sides of the neck to make it fit the dog’s body.
And you’re done…
