Wordpress duplicating images up to 10 times

Hey everyone

My site has become slow, so I've installed hummingbird and have been working on the info provided by pingdom and google speed test.

But what I've noticed is that every image I've uploaded gets duplicated by Wordpress.

As one example, this is a screen grab of the list of additional images WP has created after I uploaded "mr-lee-03.jpg" - it created all those additional mr-lee-03 images that are listed above.

Should this be happening, and could it be slowing the site down?

Thanks
Jane