A WebmasterWorld thread has Zeus, someone well known in the SEO forum space as tracking the image search engines, as not speaking positively about Bing Image Search.
The thread talks how Bing is slower than Google to index new content. Which is often the case, simply cause Google is much faster than most search engines. But Zeus breaks it out to say that their image search is even more disappointing.
Zeus said that typically he sees at most 10% of his pages or images in Bing Image search, sometimes only 5% or less. He said:
Bing Image which in my case has 45 images listed of 22,000.
Now, Bing has made some very good strides and I believe many are rutting for them to gain some more share. Heck, I even think it would be a good idea and I am an Apple guy.
Forum discussion at WebmasterWorld.