You are obligated by your contract with iStock not to do so.

Just found this... never mind..

Are there other restrictions?

    * Images, video or audio files may not be sold on the artist's own site (including collections, CD-ROMs, etc).
    * Artist may not give away files for free, from their own or any other site.
    * Rejected files may not be sold elsewhere

There are many other restrictions, which you should really take the time to read and understand before signing up:

http://www.istockphoto.com/asa_exclusive.php

Istock have rejected images that have made hundreds of dollars for me on other sites.  One of the many reasons I wont consider going exclusive.

D_mn but you're right.  I just looked at the email folder where I store istock communications and the most recent month's worth of emails contains a 90% acceptance notifications, until right around Sept. 17 it reverses to 90% rejection - including many very similar photos of the same subjects from the same shoots.  And these are IMHO attractive looking shots of rare, extremely unrepresented subject matter.  If the subject is isolated it is "too feathered or too rough" or plain old "isolation", if it is not isolated it is "lighting".  Now the second rejections are starting to pile up, sometimes with different complaints from the original rejection.  If this is happening to other contributors then I guess the scout pipeline must be stuffed almost to burst.

I get the feeling they don't want any small contributors, at any commission rate, whether exclusive or not.  Which will leave them with a small number of factory contributors shooting tens of thousands of bland, safe copycat images fethcing a high commission rate which they claimed they couldn't sustain.  Maybe the plan is as someone else suggested to eliminate all the small fry, then push whoever's left down to 20%.

I've always wondered if rejected images could be sold as RM elsewhere, or if they exclusively rejected as well.