A tag is a piece of information that you add to digiKam's database that helps you to identify a photo again in future. For example, you might tag a photo with the names of the people who appear in it, the location at which that the photo was taken, or the name of an occasion.
To tag an image, right-click on it, then click Apply Tag, then place checks against one or more tags from the list. To add a new tag to the list, click Add New Tag and then apply it to the photo. When digiKam displays the image in future, any tags that you have applied will appear below the picture. Applying tags does not alter the photo itself, and you will not damage your photo by tagging it. DigiKam stores tags separately from the photos.
To search for images with a particular tag, click the Search button, type the tag into the search box, and press Enter. DigiKam will display all the images to which you have applied that tag.