[NextGen-Galler] how to use tags?

I’ve been adding tags in the tag fields of all my images in NextGen Gallery. How do I get those image tags to show up in a tag cloud? I just installed the Simple Tags plug in and have it set to show all tags alphabetically, but on my site, nothing shows up. I’d like people to be able to view my image tags so they could click on say a D70 tag and see all images in my galleries shot with a D70.

Are tags only supposed to be done on posts? If so, how do you use the tagging feature in NextGen Gallery so those tags show up in a tag cloud?