you won;t need to pay any tax on it
each year when you send your self assessment off, just make sure you put some of your gear down as costs, and make the costs add up to more than you earn from the photos
that way you never make a profit, so never pay tax
(on the photos anyway)
and if you put something expensive down, so you make a big loss, you can carry that loss forwards to the next year
you can put stuff like fuel down too... (to go take the photos) but it's probably not worth the making it that complicated