There are several ways to add tags (or categories) to your images.
Add Tags when Uploading Images
The first way to add a Media Tag is to do so when you upload an image. If you scroll down past the Title, Caption and so on, you’ll see a field called Media Tags, with another below for Categories. To add a tag, simply type in the tag you want. If it’s one you’ve used before, you should see an auto-suggest from which you can make your selection. You can add multiple tags or categories to an image.
Add Tags from your Media Library
You can add (or edit) Media Tags or Categories to existing images in your Media Library. Access your library from the WP Admin menu. You can then scroll through or search for specific images. Once you click on an image, you can scroll down until you find the fields for tags and categories ( as in the image above).
Add Tags from FooGallery
With FooGallery Pro, you can also add tags and categories from the FooGallery Menu. Goto FooGallery –> Media Tags or FooGallery –> Media Categories. Here you’ll see all of your existing tags and categories, along with the description, slug and number of images to which each applies. You are able to edit your existing tags from this page or add new ones. These will now be available when you add your tags or categories to individual images.