Historically search engines found it hard to read any information and links that do not appear in HTML format within a page’s source code. The continuing development of Google Image Search, which is becoming integral to the search engine’s algorithms, has improved this somewhat.
AJAX changes content on a page without changing the page’s URL. As a result, search engines are unable to index this. Google had developed a way to crawl AJAX-enhanced pages in 2009, but ceased recommending the use of AJAX in 2015, although tests have shown that Google is still able to crawl these pages. In order to be certain that your site will be comprehensively crawled while still featuring AJAX, your agency will be able to build new URLs for the differing versions of your content, and conduct standard redirects to them from other areas of the site using standard HTML.
Search engines are unable to ‘guess’ at the content contained in Flash, and as a result, text contained in Flash animations will not rank in search engine results pages.
As search technology continues to evolve, search spiders are beginning to identify some of the content contained in videos and images. Optical Character Recognition (OCR) is already very much in play, allowing spiders to read images contained in un-spiderable content—to an extent.