How many friends I can tag on my Facebook photo?
Can I tag all of my 1000 friends on a single photo?
According to this Facebook Help Article, 50 photos.
You can tag up to 50 people or Pages in a photo. Some tags may not be visible if there are tag requests pending. If you have reached the limit, an existing tag will need to be removed by you or the person who posted the photo before another tag can be added.