sharing wallpapers across users

Yes, if you enable VRTY.ORG integration, you can share your profile (the wallpapers you liked) with other users.
Or do you mean uploading a new image to be seen by other users of Variety?

Yes I mean uploading new images.

I haven't yet added functionality to VRTY.ORG for uploading new images. There will be, but it will take some time.

The easiest way to do this now is to open up a Flickr account, upload the images there (if possible, best to mark them with a Creative Commons license) and then you may manually add it as an image source to Variety and favorite them (this way they'll end up in VRTY.ORG), or send the Flickr photostream link to me and I'll come up with some way to add them to VRTY.ORG.

Do you have creative rights over the images or they are collected from various places? If yes, and they are of high quality and of interest to the general public of Variety, we can add it as a default source.

Alright thank you for the advice, I will see what to do.

Email me a couple of the images you have in mind, please - peterlevi at peterlevi.com.