That’s a very important distinction. Hard wasn’t the clearest word for that use. I guess I should have called it something else such as deceptive or misleading. The idea is that some pictures got a below 50% ratio, which means that people were really bad at categorizing them correctly.
There were surprisingly few pictures that were close to 50%. Maybe it’s difficult to find pictures that make everyone guess randomly. There are always a few people who know what they’re doing because they generate pictures like this on a weekly basis. The answers will push that ratio higher.