To get Google's mobile rendering tools to return a comprehensive report, it is necessary to not block images via robots.txt. So I while ago I removed:
User-agent: *
Disallow: /images1/
Disallow: /images2/
Disallow: /images3/
...etc
Google seems to be the only one who fully supports the header X tags, where I use noarchive for image directories. Now Google requests these image files, reads the header & does not index them into it's image search.
However since image directories are no longer disallowed in robots.txt Bing, Yandex, Yahoo, et al are once again indexing these images. So I have switched to bot specific disallows:
User-agent: bingbot
Disallow: /images/
Disallow: /images/
Disallow: /images2/
Disallow: /images3/
Disallow: /images4/
Disallow: /images5/
Disallow: /quotes/
But it's been a while since I've logged image bot names. Are these still the correct names for these image bots?
Bing: bingbot
MSN: msnbot
Yahoo: Yahoo-MMCrawler
Yandex: YandexBot
Any other image bots that obey robots.txt?