Lockscreenizer is a neat little utility app that can be used to easily darken the bottom half of any image, thus making it more suitable for use as a lockscreen wallpaper. This can be necessary, especially when using your own images, because the white text and notification icons displayed on the lower half of Windows Phone 8's lockscreen can become hard to see when using lighter hued images.

In the app the degree of darkness adjustment can be changed using a simple slider control, allowing you to optimise the level for each image you wish to use as a lockscreen wallpaper. The app can also, optionally, be set t cycle through a collection of images, so that your lockscreen wallpaper is automatically refreshed periodically.

There are a plethora of apps with lockscreen integration available for Windows Phone 8, including a number that let you cycle through your own images, but Lockscreenizer is noteworthy for being relatively simple, while still providing a fix to the most common issue with using your own custom images. 

Windows Phone Store description:

This app lets you selectively darken portions of photographs and pictures to make them more suitable as lockscreen images, and will also optionally cycle through a collection of chosen images.

Lockscreenizer is a free download from the Windows Phone Store.