Its due to the depth of the images. The higher the number the more it'll move.

Thanks Peter b ps know a good screen recorder to make that video

I use fraps, but thats not free.
An old free one i used to use was: http://www.koyotesoft.com/video-software/free-screen-to-video.html

how do I put custom images in?
if I do how will people who download my level pack get them?

To use custom images in your level you should probably just put them in the level directory, then import them through WooGLE. When you create the goomod WooGLE will automatically put them in the level folder along with the other necessary files, so that people who download them have them.

Thanks puggsoy!