1. Image upload screen provides textarea for entering comma-separated keywords
2. User matches keywords (called tags on this screen) to terms from controlled vocabulary
iStockPhoto provides an interesting way of mapping keywords or tags to the controlled vocabulary the site uses. This makes a lot of sense in a site that wants people to be able to browse for concepts, themes, and subject matter with a high degree of relevancy. Curiously, they refer to the keywords as tags on the review screen when the term "tag" isn't used on the site as of this writing.