Like in reCAPTCHA (v2 at least) where it asks users to click on tiles to identify common objects like bridges or motorcycles. Surely one could conjure up a fake version of this.

I've seen people complete actual CAPTCHAs that were something like "Click here exactly 10 times to prove you're human" so I don't think you'd need anything fancy. People wouldn't stop to question it and are used to doing much weirder CAPTCHAs without understanding what they're for.