Bing Preview = preview in SERP & source preview in Bing Image Search results, but the bot scraping your images for the Bing Image Search is Bingbot, not BingPreview.
Thus - blocking BingPreview will not stop Bingbot from scraping your images nor get them removed once they're in there. In fact, if your images are *already* in the Bing Image Search results, blocking any of the Bing bots will not remove these images, only stop them from being removed.
The only way to get Bing to remove your images from the Bing Image Search results is to allow Bingbot to crawl these images again and to *now* use the NOINDEX X-Robots-Tag HTTP header for your images, but NOT for the web pages themselves. This is important since blocking Bingbot from crawling the web pages containing the images will stop them from updating the index status of the images.
These are the exact words from my guy at Bing when I asked him on Dec 20.
If using Apache server (and if your config supoports it) add this to htaccess file in each image directory (not the base htaccess file):
Header append X-Robots-Tag: noindex
(then access your image file using a header checker tool to check and see if the NOINDEX tag is being included. If not, check with your server admin for the proper way to include it.)
Note - IMO using the NOINDEX X-Robots-Tag HTTP header it will still take 30 to 90 days for your indexed images to get removed from Bing Image Search.