When I enter the exact string "bed design ideas" into google images it includes pinterest results, while "bed design ideas -pinterest" excludes them. Is there a specific failure case for you?

-site:pinterest.com

works perfectly, and i use it in my all queries where i search for images.

This should be the default, TBH. Why google thinks that an image search leading to pinterest is going to be helpful is beyond comprehension.

If the original source is still online I indeed prefer it, but occasionally some images of interest only survive on Pinterest, in which case a Pinterest result is better than nothing.

Another thing is probably how images are indexed in the first place. Historically image search could only look at the text surrounding the image (and the alt-text, if provided) to get some sort of tenuous idea what an image was about. Pinterest provides some additional tags for each image, which can help make it more discoverable.

Of course these days Google also runs image recognition (and OCR) on the images it indexes, but I suppose sometimes the tags added by Pinterest still provide some additional context without which the original image wouldn't have been found.

>Why google thinks that an image search leading to pinterest is going to be helpful is beyond comprehension.

Both founder/ex ceo and current ceo came from Google. Pinterest directly deposits >$xxxmil/quarter into google.

I've found that sometimes I have to also exclude specific "*.pinimg.com" (or something similar; don't recall the domain for certain offhand) domains, especially when doing an image search.

I use two Chrome extensions “Unpinterested!” for Google and “Not Pinterested” for Ecosia that both remove Pinterest’s search engine effluent from results.