The DuckDuckGo logo changes depending on search terms

This is new to me, even though I use DDG as my daily search driver.

I was searching for some sailing engineering techniques in historic contexts when I noticed the DDG logo in the top-left change to the appearance of a pirate. Thinking it was by chance (while forgetting what an actual stereotypical pirate looks like) I typed in "jack sparrow" as the search term, just for fun. The DDG logo itself updated again to match his appearance.

The same went for wizard, harry potter, etc. where the DDG logo's appearance matched the search terms.

Again, I might of not noticed this despite using DDG every day, but does anybody know how long has this been going for?