Slideshow on lock screen???

Hi, when I first got my phone (about a month ago)I set a photo from my photo library as my wallpaper for my lockscreen and homescreen. This has been fine, but this morning, for some unknown reason, my lock screen now shows a slideshow of the album covers from my itunes folder. I can't work out why it is doing this, or how to make it stop. I have tried simply just going back into settings>wallpaper area and resetting my photo as the wallpaper, but this doesn't seem to overide the slideshow. It is very odd, as it has seemed to do this without my having changed any settings myself. Any idea what is happening, please?