The first and at one time largest of the microstock libraries. Now part of the Getty images empire. Since 2003 we have watched the cost of photos steadily rise (good news for photographers), gone are the days when you could get a good usable image for $1, they introduced XSmall images and in effect the cost of an image tripled overnight. In early 2010 exclusive images doubled in price making istockphoto very attractive to those who are willing to tie their images to just one agency.
Overall the site is very popular among buyers having an almost cult following, if difficult to get images accepted; you should include iStockPhoto in your portfolio. Don't lose any sleep if as a non exclusive you earn less on this site than on some of the other smaller sites. Following a change to their best match algorithm in early 2009 I have seen good returns throughout this year (2009). This might also be partially due to getty cannibalising traffic/adspace/sales that were previously covered by Stockxpert, Stockxchange and other ex Jupiter Sites.
The Killer Search

From what I can see istockphoto has pretty much the best search technology I have ever seen at a microstock agency when it comes to a buyer finding images. It makes it slightly more difficult to upload to as you have clarify the meaning of your keywords. for example include a keyword 'orange' and you will be asked to tick one of two boxes Orange (Descriptive Colour) or Orange (Citrus Fruit), or perhaps you include the keyword 'lead' the response will be Lead (Metal), Dog Lead (Pet Equipment), Leading (Moving Activity), Graphite (Material) etc and the list goes on for 1000's of different ambiguous words in the English language. This really is cool stuff, as an image purchaser trying to clarify exactly what sort of image you want using words is a difficult business and this helps significantly.
Exclusive Photographer? 
A big decision for any photographer to make. Becoming exclusive with istock will mean that you cannot upload images to any other site. I can't comment on what its like to be exclusive as i have no experience, many people swear by it. exclusive photographers get a larger percentage per image purchase, and also receive 'care' from the site - istock will chase people who use your images in breach of the license on your behalf. You will also come across 'Exclusive+' which allows exclusive photographers to nominate a small ammount of their images for sale at a higher price.
The top exclusive photographers also get to sell their images via getty's image network (including photodisk) increasing sales potential dramatically.
Audio, Video, Ilustration, Music, Flash, Logos... 
Along with several other agencies istockphoto also accept video and vector illustrations. They have recently launched their new audio library 'istockaudio'. Even if you only contribute photographs to istock it's important to consider that buyers may find istock a convenient one-stop-shop for all their media needs, and these buyers will be your potential customers.
It's true that at present many buyers are only in the market for images, but demand for video is growing fast and commission rates are higher. I can see one recipe for success in this emerging market is having quality video with matching print resolution images, hence designers can create matching online video and web/print campaigns; perhaps even just the option to go back and download matching images if they become needed will be enough to make your video work stand out.
istock Tips 
Uploading
Istock is the only major microstock site that does not support FTP/SFTP upload. There are a couple of work-arounds for this. Firstly there is the istock image manager available for download from their site (istockphoto.com/ws_client_intro.php). The second option is to use isyndica to submit images but make sure you log into istockphoto and set those categories and keywords once the upload is done. The third option is a simple time saver: bookmark the page that is shown when you have clicked “upload > image type” (the one with a browse button) put the bookmark in a shortcut bar in your browser, then once you have logged in you can click it and save yourself a couple of clicks and page loads for every image you want to upload i.e. just click that shortcut when you receive the upload confirmation page and you are ready for another image.
Promotion
I stock has a several useful features you can use to increase your sales. First up you can embed simple html into your image descriptions, these can be used to direct potential buyers to other images that you have uploaded that match the image, i.e. those in the same series or of a matching theme. You could also create a small banner for a public lightbox and link to that from the image description (that way the code is the same for each of the related images). You can see in the example below the photographer has linked to several related images in the description:
Another useful promotion tip is to either create a couple of ‘visual blog posts’ in your personal istock blog that link to either a lightbox or some recent images. Other similar options might just be including thumbnails to a select number of your favorites. Either the blog tab or the profile tab (if you have not created any blog posts) is displayed to visitors when they arrive on your profile page – this is the place to sell yourself. Buyers are interested in the quality (both technical and artistic) and choice of images you have, try to emphasize those as key selling points.
Conclusion
Despite my criticisms of this site, the low commission level (although fotolia recently dropped their basic commission to 25%), restrictions on the number of images that can be submitted (for full time microstockers istock is quite restrictive) the fact that it has fallen from the #1 spot, tedious keywording process etc, I still recommend istockphoto as one of the top four earning microstock agencies. The microstock market moves and changes all the time, a brief look at istock right now (Dec 09) shows them to be my top earner despite worse results from 2008 where they were trailing around 3rd.
August 2010: I stock announce that they payout over 1.7 million dollars every week to their contributing artists.




is it still possible for amateurs to join?
Ronnie Hall (not verified) on Tue, 11/10/2009 - 11:26Joining
Steve Gibson on Wed, 11/11/2009 - 01:58Bad
Henri Faure (not verified) on Tue, 11/17/2009 - 13:04don't don't
Steve Gibson on Wed, 11/18/2009 - 02:47Exclusive Contributors
Alistair Shankie (not verified) on Sun, 01/10/2010 - 19:00