Here is how to do it:

1 – Open your image
2 – On the top menu, go to Commands > Creative -> Fade Image
3 – A dialog box will open, choose the kind of fading effect that you want
4 – Click OK
5 – If you select your image, you will see a line with a dot and a rectangle on each side, hold the dot and move it around and experiment. Use the rectangle to move the whole effect around and the dot to resize it and change it’s direction.

Enjoy