There are numerous apps available in the Windows Phone Store to help customize your lockscreen. Awesome Picture Quotes (formerly known as Wallpaper Quotes) is one of the newer offerings that delivers picture quotes for your lockscreen. The quotes are often accompanied by a inspirational photo or drawing as well.
Available for low-memory devices, the interface is simple (maybe too simple) and the collection does have some nice looking images with inspirational quotes. Awesome Picture Quotes is a nice foundation for a lockscreen app. has a slight level of appeal but could use a little polishing.