Assuming there is no og:image or link rel img_source, does anyone have any real-world experience or advice on better-than-random techniques to choose an image that best represents a web page?
Update: All answers are good, so upvoted them all and selected one, although it seems there is no great way of doing this. I will experiment with largest picture and screenshot of what it would like on a low-res client. Thanks all!
PS: I’m finding that quite a few pages seem to have og:image or link rel img_source anyway. More than I expected
Taking a screenshot of the website in its smallest possible form, how it would look on a notebook laptop or even a mobile (but not the mobile site version), would be a non-random approach.
Most good web designers will try to make sure users are able to see what the page is about immediately upon loading and include the most important and relevant information ‘above the fold’ as they say.