[jononor]

It is just a consequence of other humans also having problems with these cases. They do not mind that you have to make multiple attempts, it is just more yummy data for their bots (their machine learning algorithms are trained on this stuff).

[mehrdadn]

I'm pretty convinced they're not really using these for ML, but that their ML algorithms have already run on these and they already know these difficult (read: ambiguous) enough to make you give up. These cases specifically only come up when they seem to think you're probably a bot (based on cookies or IP or whatever). They seem to deliberately put the photo boundaries such that they slice through whatever object they want you to look for. And they intentionally make the delays extremely long. These don't happen when they think you're probably a human and just want to throw an extra hurdle (like if you're Googling a little too frequently from your usual browser/location).