The many images are the optimized versions to use in the gallery. If you are uploading photos, the space of the original image is probably greater than the sums of the spaces of all of the copies. If you tried to use the original image and it was a photo, it would be way too large to display on a web page.
If you are only using a particular size in your gallery, then you could update it to only create that particular size and not the other versions.
Can I get FTP access to your server? I'd like to take a look at what you have and I can potentially suggest a solution. What version of powergallery are you using? How large are the original files you are uploading? If I get FTP access I can answer these questions for myself.