While pictures would be under copyright (and it's possible copyright is with a third party specialised in this), I can't see how the price listed for a product on, say, Tesco's website and collected by yourself on Tesco's website could be subject to licensing by a third party, even considering database rights.
I am also puzzled by those guys claim that they got a very "generous offer" from that company.
If they are unsure a better first step would be to crowdfund legal advice.
They could then crowdsource taking pictures of all the products from their users.