using gallery to archive webcam images

I have a webcam that updates every ten seconds on my website. I'd like to create a gallery of archived webcam images, where images are added to the gallery by a visitor clicking a link under the webcam image on my homepage. I want this to be an easy, two-step process:

1) click the link and the 'add photo' box pops up.
2) the visitor fills in their name and a comment, and clicks to upload the picture to the gallery.

there would then be another link below the webcam to take the visitor to the gallery, where they can see and comment on all of the images others have put up.

I see a couple of problems in doing this that I haven't figured out how to get around:

- I would like to have it so that the visitor does not have to register with the gallery. It's too much hassle to sign in each time, and they will most likely miss the image they wanted to capture anyway.
- I would like to have it such that, when they click the link to add the image, they only have the option of adding the image from the webcam (or, ideally, a copy of the webcam.jpg file that existed when they clicked on the link) and no other images.

If anyone knows of a way to implement my idea, I'm very open to suggestions!