This may be a dumb question, but I really have no idea and I’m utterly curious! So please bear with me.
What I know is search engines just read HTML and words in a site. They usually ignore CSS or part of it. They arguably cannot read images. Do they?
If they really cannot or ignore to read those, then my question is how do they make screenshot, which is a page that is presented just the way as CSS makes it, and has images.
If they do not read CSS, images, and they also do not like human being to open it in his or her screen. How do they make the screenshot?
Thanks!
Are you referring to Google’s new screenshot feature, or their old cache feature? Your question is talking about screenshots and doesn’t mention the cache at all, but your comments on your question seem to imply that you’re referring to the cache, not the screenshots.
In the case of the screenshots:
You are correct in that search engines usually only read the HTML and text on a website, because that’s all they need. But that doesn’t mean they can’t.
When they want to take a screenshot of a site, they’ll just do exactly what a normal browser does when a user visits the site. Download the website, the CSS, the images, and everything else, and render it with the rendering engine of a web browser, such as WebKit.
In the case of the cache:
The search engine usually just stores the HTML without/before parsing it. It sends the saved HTML to your browser, and your browser pulls all the other stuff in the page (images, etc) from the original website. The search engine isn’t reading anything, it’s just saving the page verbatim (well, with minor changes, namely URL rewriting), and giving it to your browser.