In the UK, debt collection agencies are licensed and regulated by the Office of Fair Trading. The OFT sets guidelines on how debt collection agencies can operate and lists examples of unfair practices. These guidelines are not law, but do represent a summary and interpretation of various legal areas. Compliance with these guidelines is also used as a test of whether the agency is considered fit to hold a credit license.
Examples of unfair practices include misrepresenting enforcement powers (e.g. claiming that property may be seized), falsely claiming to be acting in an official capacity, harassment, claiming unenforceable or excessive charges, misrepresenting the legal position to a debtor), and falsely claiming that a court judgement has been obtained when it has not.
Collection agencies in the UK should not be confused with court-appointed bailiffs.
They cannot forceably take property seize goods or hassle you into giving money. They HAVE to get a court order to do so.
Getty/Corbin are using scare tactics, the debt collectors (if any) they employ will also try to use scare tactics. You have to play them at their own game. Obviously, to work for major companies like Getty/Corbin, you would have to be legit, so use the scare tactic on them of having their credit licence revoked.
I would also add that due to the complexity of UK law, the chances are really slim they would employ a debt collector anyway, unless you are just taking the persistant pillaging of their images.
I found time and time with people that host websites with me that if they remove the images and then do nothing, everything stops.