Very different, to the degree that if you were offered one and given the other you'd be confuse (but of course, you wouldn't vocalise it).

Sarcasm, if this is sarcasm, doesn't scale well across cultures, and especially not online, in addition, in text form :-)

That's if you're being sarcastic in addition to OP's original comment.

This is not sarcasm. I have a distinct idea in my head of what a cookie should generally look like, and it doesn't look like a biscuit. I can see the confusion, both have chocolate chips in and your classic digestive usually doesn't, but I'd put good money on my ability to identify one or the other

It's definitely sarcasm :) Most Brits would likely identify the first link as "cookies" too (based on their appearance at least)

No, they're very different, but I agree that the pictures look alike.