How to Untag Someone You Tagged on a Wall Photo on Facebook
You can add Wall photos to your own profile, or a friend's profile, so long as she has not restricted people from posting to her Wall. Anytime you apply a tag to an image, the person you tag receives a notification about it. Both you and the person you tagged may remove the tag with a couple of clicks.
Go to the Wall photo in your Web browser. If the photo is on your own Wall, click the "Profile" link in the Facebook banner. Click the name of another user to access that user's Wall.
Click on the thumbnail version of the photo on the Wall to open a full size version.
Click the blue "Remove Tag" link to the right of a user's name under the photo. The tag is immediately deleted.