I just thought I would drop a note in here and stress the importance of good keywording. You will find that many agencies are starting to consider the keywords you use when deicding whether to accept or not....

I agree, be very careful with the words you use. Many times we use keywords that are only "related" in our minds. If there is not a cow in the picture of milk, than you probably should use cow in your keywords.

I have had a few messages on Dreamstime and iStock that said (pretty nicely for now) that my keyword have been "adjusted" to match my picture.

I agree, be careful, but don't stop being creative. I try and have 30+ words per photo. No keywords=no search findings.