No, but you can suggest tags for them. To do this, click on the "Tag This Photo" link when you are browsing someone else's album. To tag the photo, simply click on a person's face in the photo, and then select their name in the box that pops up. If their name is not already in the box, you can provide it. Repeat this process for everyone in the photo. If you need to tag yourself, select "me." Click the "Done Tagging" button at the top of the page once you've finished entering your tags.
When you tag another person's photos, no one will be able to see that tag until the tag is confirmed by the person who uploaded the photo.