You might want to expand this article to bring text-shadow into the discussion. Many of your examples are illegible and as such complete failures at the most basic of accessibility concepts. A simple text-shadow can work wonders to make things like your "final result' and the one before it not be a giant middle finger to usability and accessibility... what with the "bodies' part of "antibodies" and the "nd im" from "understand immunity" begin far below WCAG minimums.
Much less the utterly illegible train wreck disaster that is the date in the top right corner or the about/when/shares bottom left.
It's part of why text over images are usually a bad idea, and really needs to be handled with kid gloves.
NEVER forget the WCAG minimums... and if you're having trouble keeping track of it or figuring out when it's going to be a problem, use a tool like the one at webaim to help.