I have licensed my images to a number of companies over the years, from books to newspapers to company promotional materials.

You should definitely maintain copyright. Charge them a licensing fee for the use of your images for a specific purpose (e.g., web site or print). If it's for print, you can limit it to one printing or allow them to use it for future editions of the same book. You should also ask (demand?) that your copyright notice be included with any usage of your pictures. If used on a web site, ask for a link back as well. :)

What he said..always retain copyright..always license use for very specific purposes and print runs ( if they don't know how many ..give a max figure )..if it is web, usually limit to only one domain, ( you could serve them from your own server, if you go for a numbers deal you get to see the number of "calls" ) and only to a certain size or certain sizes..

To get an idea of the usual contract restrictions go to any of the main photo stock image sites, look at their offers re sizes, limitations of use etc..read their TOS..go to more than one..specify "in case of disputes" which court system ( where ..usually the nearest to you UK ..your nearest large town, non criminal court ..would be best for you ) will be considered to have sole competency to regulate disputes..

Yes ask for link back and credits..and for your exif data to be preserved in all the file headers..agree with them a small visible copyright "you" with date on each image if possible..you may get more other work out of it from their visitors..

IIRC the UK has a pro photographers association , with website ( can't remember it's name ATM ) which had ( has ? ) advice and sample contracts for this sort of situation ..available for non members / non "Pros"..

I use pictures to illustrate locations covered in the website, and it works well, by which I mean they rank, people look at them, and then they often click elsewhere in the site. I'm not a pro but I use pro equipment and my photos are ripped off left, right and centre. I always watermark them quite prominently with the site url and a big copyright symbol, and most of those who steal them don't seem to know how to delete this. Occasionally I sell a copy - some agencies will happily pay a reasonable fee if they really want the pic, but most small businesses think anything more than about £5 is too much, which isn't worth raising an invoice for. The revenue is probably less than 2% of the cost in fuel (to get there) and equipment - and I'm totally disregarding the cost of my time in this equation.

However they can be fantastic link bait, and you can call the shots. In response to 'Can I use your picture of (whatever)', I reply, 'Yes that's fine, but if you do I'd be grateful if you'd link back. Here's my suggestion for the link: [(whatever),...] anchor text (whatever)', provided as html so they don't get it wrong. It works completely as intended 95% of the time.