Sometimes photographers or clients don't or won't understand what is being charged for and why. There are misconceptions about copyright, usage and licensing which are potentially financially damaging to either the client or the photographer.
The one people seem to have most difficulty with is copyright. The second a photographer releases the shutter he/she has created a work and owns the copyright to that work. In the UK you need do nothing more at this stage. The copyright belongs to you and you do not need to register it or take any other action to retain that copyright. Owning copyright means you are in control of all copies of the image, only you can authorise the creation of more copies.
Creating the image is a bit like building your house. You come up with a design, plan it and build/create it. At this point you may be thinking 'Aaah, that is why photographers charge a fee for creating an image.' That fee is to cover the work and creativity in producing an image. You may have been thinking that but probably you did not so that was a little prompt just to make sure we are thinking about this in the same way. When building a house it is usual to employ an architect to do the design work for you. The architect will charge for his/her creativity and design work and will also retain the copyright to all plans they produce. When employing a photographer it is basically the same. The creative fee is to recompense the photographer for using their creative skills to build an image.
Having created an image and owning the copyright to that image the photographer can now let others use the image. The user of the image will usually be the person or company who commissioned the image. For this usage the photographer will charge a usage fee based upon type of usage, duration of usage, circulation figure (number of times the image will be used) and geographical area of usage.
If the image features recognisable people, property or buildings the photographer may require model releases for each of these before usage can be offered. This largely effects commercial usage but can be a requirement for the photographers own portfolio use especially as a lot of portfolios are now displayed on the web. As a rule of thumb releases will always be required when the image is to be used commercially, may be required when the image is used as art and will not be required when the image is used editorially.
Owning the copyright does not mean you can do what you want with the image. Without model releases you have the copyright (no one else can take or make copies of your image) but you still may not be able to use the image.
If you sell or give away copyright then you cannot even keep a copy of the image you created without a usage licence from the new copyright owner. A number of competitions are copyright grabs. If entering a competition read the terms very carefully. You may find you are giving away copyright or giving an unrestricted and perpetual usage licence to the organiser. Another little term which creeps in is that you will assume all responsibility for any subsequent actions against the publisher. So, they nick your image, use it and get sued by someone and you carry the can. Seems like a fair swap for free entry to 'World of Nappies' for you and your family for the next year if you win. A lot of these 'competitions' grab these rights on entry to the competition so win or lose you have lost your image or given away a bucket load of rights just by entering.
The above is not definitive and if you have any doubts about ownership, copyright, model releases and usage licensing then you should seek expert qualified advice.