http://www.google.com/insidesearch/features/images/searchbyimage.html
Download this to your Google Chrome and then start searching for your images online and claim what is rightfully yours from those thieving bloggers.
This line always works : You ought to have known that the image would be protected by copyright, and use of my image in this way by you would be a criminal offence under S.107(2A) of the Copyright Act 1988, punishable by up to two years in prison and/or a fine.
Email me at my office if you need any help. I found over 300 uses of one picture stolen from a newspaper from the 2010 FIFA World Cup Final. A German colleague of mine now claims to have 25% of his income from stolen picture payments.
Hmmmm. I really wouldn't go quoting Sect 107 at bloggers or any other online infringement to be honest - you are likely to get laughed at.
Sect 107, and the rest of the Offences clauses, are designed to counter a specific area of infringement; namely massed reproduction, distribution and sales of copyrighted material.
Standard copyright infringement is not a criminal offence (crime), does not carry any attached fine and certainly doesn't have an attached prison sentence. It is civil law and as such attracts damages only.
If you want to get heavy, as opposed to just presenting an invoice for unlicensed use, then at least know what you are talking about...
'Unlicensed use, ignorance is not an excuse', is covered in this case:
http://www.swanturton.com/ebulletins/archive/InnocenceIsNoDefence.aspx
The best guide to chasing unlicensed use is here, on EPUK:
http://www.epuk.org/Opinion/994/stolen-photographs-what-to-do
and an overall summary can be found here:
http://www.epuk.org/News/1003/copyright-in-the-21st-century
In short, don't make up some legalese sounding stuff when it comes to dealing with infringement. If the case ends up in court then you are going to look like a tit and may well have the whole thing thrown out.