What are popular tags in Flickr?

These are your 30 popular tags. On the basis of the tags used in all your photos, Flickr selects the 30 most popular ones from all the tags. The tags with a green check mark indicate that all the photos selected have that tag, tags with a grey check mark indicate that some of the selected photos have that tag. If you tap on a tag with a green check mark it will change to a red X to indicate that this tag will be removed from all the selected photos. If you tap on a tag with a gray check mark the tag will change to green to indicate that all the photos selected will have that tag, if you tap again the green check mark will change to a red X to indicate that the tag will be removed from all the photos, if you tap again the red check mark will go back to the gray check mark, so nothing will change.