As i need to add writing to the back of my dvd cover and the background is quite busy meaning it would be hard to read, i made a black rectangle to put the text on at the back

 However I felt that a solid black rectangle looked quite messy so I then decided to adjust the opacity so you can still see the background image but if i overlay white text it will be easy to read.

I am pleased with the effect this has had once I added the text to the back.