If you only need a few keywords, the much-neglected Label feature of the finder can be surprisingly helpful. You can also add any text in the Spotlight Comments panel of the 'Get Info' box of any file or folder. I'm not a Spotlight guru and, on the face of it, searching on the Comments panel seems to be not exactly a one-click process. However, if you plan to use it regularly, I'm sure it could be streamlined.
If you use iPhoto then search the Help files for 'Assigning keywords or checkmarks to a photo.'
In Picasa they are called tags.
The advantage of Picasa [apart from being free & neat] is that it does not store your pictures but simply references those you want it to where-ever you might chose to store them. Tags that you apply in Picasa can be found through Spotlight.
Many thanks for the replies but I should have stated that I have to keyword all my images which I submit to a picture library. So it isn't for searches on my computer but for potential clients who are searching for particular images in the library online. There is a Windows based solution at: http://www.imagekeyworder.com/default.aspx
but so far I haven't seen anything like that for the Mac.
Thank you Mark. I have looked at a few possibilities from the sites you mention and downloaded one as a trial. (Stockphoto Catalog). Unfortunately I haven't found quite what I am looking for yet. Several are plug-ins for iPhoto which I don't use much. I use Photoshop Elements with Bridge for most of my images. I will keep looking and thanks again.
If you use Bridge, you can use that to append keywords.
Go to Adobe Bridge - Tools - Create Metadata Template. In the resulting dialogue box, select IPTC core, and tick the keywords line. You can then type your keywords in the box (you may want to take the time to apply a copyright to your piccies at the same time)
Then, once you have made the template, select your pictures and go to Tools - Append Metadata, and Robert is your close paternal relative! If you need different keywords for different images, just edit the template.
If you want to use different keywords all the time, just make visible the keywords panel in Bridge, and edit/use accordingly. This involves creating a whole list of commonly used (or not so common) keywords, selecting a photo, and ticking the appropriate keyword(s) for that image. That keyword(s) will then be appended to that image. Shheemples!
Bridge is a powerful tool, with many hidden tools - have a play before you fork out on other programs.
Roy Rainford 