The problem I faced: I was scrolling through a hashtag‘s timeline in Tweetdeck, when I spotted a nice image. I wanted to retweet it, but that failed: turns out the tweet was deleted in the meanwhile. This usually means that either the artist themselves deleted the tweet for some reason, or it was stolen in the first place and (by some miracle) it was moderated.
In this case it seems to have been the latter, so finding the image through the author’s profile was not an option. As Tweetdeck displays images as CSS backgrounds in the timeline, right-click “Open image in new tab” was not an option. Since the tweet was deleted, its URL was invalidated too, so I couldn’t give that to Saucenao or similar to find matches either.
However, while digging through the Firefox Dev Tools, I noticed that the context menu when right clicking the URL of the
background-image had an item “Copy image data URL”. This turned out to be just what I needed.
Pasting the copied (data blob) URL to the address bar I got the image that I could magnify so that I could decipher the artist’s signature on it. (It turned out to have been a partial image so Saucenao couldn’t help either.) After a few tries I found the artist’s profile and there the original post. Yay.