Blur

Going to add a space ship to back cover and give it a blur to give appearance of movement.

Starting Image: 

It has a purely white background so cut entire thing out with Magic Wand.

On cover:

For this to work well, I duplicate the ship layer.

Now with the lower ship layer selected I go to Filter > Blue > Motion Blur



A window then appears which allows me to alter the angle of the blur and the distance it effects. 
I set the angle to 27 which lines up best with the ship, and increase the distance to 406. The small box on the blur window shows what the image of the ship looks like, but I have the duplicated layer showing on top so I can line up.

I tried the blur on just the bottom of the ship
 but it is too subtle



So I'll stick to the full blur, ad will cut off the parts of the blur which go up instead of down, as even though it is a movement blue and you pick an angle it blur it in both direction.

to cut the excess blur out I used the lasso tool.