You have a free software Winwall, which lets you, randomly or at regular intervals, change your wall paper. Its user friendly interface provides you with a wide choice of functionality at the same time brings to you the best quality software in desktop wallpaper management, definitely much better than the windows default wallpaper manager.
You have the choice of either manually adding images or allowing Winwall to do it for you, by letting it search your hard drive for other alternative file types. It also comes with the ability to load images directly from the internet to utilize live feeds from across the world.
It shows BMP, JPG, GIF, and PNG images through both random and sequential order. Also, if you are one of those who like to customize according to your taste, WinWall provides various switches to make the necessary adjustments enabling you to enjoy its benefits to the maximum.