Leaf asked a good question in the Earnings thread this month - do we need to add new images to maintain our earnings, and so I decided to analyse my Shutterstock earnings a bit to see how those have changed as I added new files, and how the percentage of earnings from the different categories of download changed over time. I then started a bigger bit of analysis to look at how the earnings per online file at the main agencies has changed. I use online files per agency as the indicator here, not total available images, as I know that some agencies (Fotolia and Dreamstime) don't like certain types of image and it seems wrong to penalize their performance because of that. I could choose not to upload certain types of image, but it is easier to upload the lot and then let them reject the ones they don't like.
Anyway, fuller analysis is on my blog as usual, but here are the highlights:

This graph just shows my earnings activity on Shutterstock - hard to see much detail, except that I have been working hard!

I then looked at how the earnings changed by category of download, and then turned that into a percentage graph to see if things had changed much over the past 2 years:

This seems to show that, on average, subscriptions give me 50% of earnings, ODs around 30%, and, although my EDs have dropped off since June 2012, Single downloads have picked up to make up the remaining 20%. It varies a bit from month to month, but the basic pattern holds.
My final graph is a work in progress as we are only one month into Q4 of 2012, but this shows the earnings per online file at the main agencies (and then a total for the "rest"). Again, there are ups and downs, but the basic pattern of $0.60 to $0.70 per online image per month is being maintained.

I'll come back to this analysis in January 2013 once Q4 is complete, but it appears to show a reasonably straight line relationship between online images and income. Add more images, get more money - things are neither getting better or worse for me in the microstock game in terms of income per accepted file.
Steve