The "whitish" is the transparency of the image.
Depending on how you set the wallpaper image sometimes you don't get the option to change the transparency.
Some photo software allows you to set the wallpaper image and adjust the transparency that way.
If yours doesn't allow that, try
Resco Photo Viewer, it's a great program.
It has a free trial so you can use it to fix your problem without having to buy it, But it's well worth the money.
Sorry, added the link, forgot it the first time.