Yes you can tag them, but you’ll have to do it after you load the image. Once you add the image then you can go to the image click on it and then select edit. Add the fans/friends on the line that says: Who are you with. Now if you’re adding the image from a mobile device you can tag someone immediately. 

There is no way to tag Page Fans yourself, @moinshaikh – they have to tag themselves.  Make sure you have the Photo Tagging option checked on the manage permissions page in the Edit Page area.  Then just post a message asking them to tag themselves.