The man uploaded the image a a joke, and panicked when he realised he couldn't delete the image. In court, he admitted the charge of "causing the display of indecent matter". The image was only seen by Tesco workers and not by members of the public.
The sentence includes 100 hours of unpaid work, a victim surcharge of 60 GBP and costs of 85 GBP.
Of course, the Tesco store, like most supermarkets, probably sells the Sun newspaper (prop R Murdock) with its famous (and ongoing) page 3 (NSFW).