Which module to enable?

I placed the module in my module directory, and went to enable it, and there are two option lazy image loader and lazy image loading. Initially I enabled the lazy image loader, but didn't see anything happen, then I went to enable the lazy image loading module, and my site crashed by saying a function had already been declared by the other module. So I got rid of the lazy image loading module, and my site came back to life. Can you please clarify what is going on here? Thank you. I really appreciate the module.