Pfui - 6:37 am on Nov 29, 2010 (gmt 0)
One "url(data:image/png;base64 (etc.)" sighting here in the last hour:
Google Referer? No (no ref)
Google TB? Yes: GTB6.6
Apparently Real? Yes
Notes: Multiple images on page but "url(data:image/png;base64" appeared only once -- 30 seconds after the visitor first hit the page -- not beforehand, as would be suggested by their clicking on a Google Web Preview icon/image and then visiting the page.
Speaking of... Google Web Preview [webmasterworld.com]
@DanTheWebManSRQ: A 404 server response is proper, and methinks preferable to rewriting the pattern to anywhere (let alone to Google -- oy).
If these mystery URIs get out of hand before whatever's causing them gets fixed, I'll be tempted to suppress them in my logs because they're so danged long. (At which point I'll hope jdMorgan [webmasterworld.com] has already weighed-in:)