It doesn't look a conspiracy, TBH.
Search engines like "duckduckgo" or "qwant" return similar results when I search for "white couple" or "historical europeans"
As far as I'm aware all three index the www on their own.
If a page contains the word "white" and the word "couple", it means that it has a racial connotation, not that it contains an actual white couple.
As for the rest of the search terms, it is possibly only a tendency. I don't know how exactly the indexing of images at Google works and it's not supposed to be a public information anyway. Maybe they index the context of the image, being the text surrounding the image and its URL. Maybe they look for metadata in the images or actually process the whole bunch and what not... But anyway, I suppose spamming a large number of forums, blogs, websites with these exact terms could tweak the results ranking.
Also, yes, Google removes many results that others do not. Just try to download a film and be surprised how hard it is to achieve it with Google as starting point and how easy it is with any other search engine.
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