Interesting data, but one disagreement. Percentages don't match this kind of information. Whole numbers do.
Milestones:
September 21, 2006 - Shutterstock surpasses one million stock photos
Feb. 20th, 2009 -Shutterstock reaches 6 million photos,
February 14, 2010 - Shutterstock reaches 10 million Photos
June 19, 2012 - Shutterstock reaches 20m stock Images
October 30, 2013 - Shutterstock reaches 30 million images
Aug. 4, 2014 - Shutterstock celebrates 40 million images in it's collection.
Prediction at this rate:
April 2015 50 million images.
Dec. 2015 60 Million Images!
While your point is the percentage of new images has dropped, with larger numbers as the collection grows, percentage does address that in
nine months: 2013-2014
Ten Million New Images got accepted!
It took 16 months for the ten million before that and 29 for the ten million before that, with something like six years for the first ten million.
When it hits 50 million, the percentage growth will be smaller, because it's a smaller part of a much larger number. But the ten million images, is still another ten million!
We aren't competing on percentages, we are competing with whole numbers. What is a percentage, which is shrinking at a rapid rate is, our individual percentage of the total images.