By default you are not allowed to setup a separate wallpaper for your Lock Screen and home screen on BlackBerry 10 OS. If you go to Setting and choose one picture to use, it will show for both of them. If you would like to make one wallpaper for your lock screen and another one for lock screen, one of the best solution is to use Screen Lock App for BlackBerry.
I tried a few free and paid apps in appworld. Some don’t really work or aren’t worth mentioning. Finally I got this app called Lockscreen Wallpaper – with Picture Frame by Bellshare GmbH. It is pretty much everything I need.
Lockscreen Wallpaper app not only lets you setup separate pictures, but also show your photo library in Lockscreen Wallpaper’s active frame. The picture frame functionality features any folder (include all subfolders) to use and changing photos with customizable interval time.
Due to the limitations of the current API’s, you need to run the app in the background. It’s ok, but not perfect. Because it lack of font size selection. Download Lockscreen Wallpaper from appworld.