Not all pictures of targets are brag groups, but I get it - It's a forum. There will always be those people that whenever an applicable thread occurs, will post their same old "good shot" groups. It's like if you searched a specific topic, you might see the same photo(s) in every thread.
Credibility is a factor too. The individual who posts groups or ammo combinations that didn't work as well along with the ones that did provides far more information and attains a greater level of trust than the poster who just shows a "highlight reel" of cut targets with bughole three shot groups.
Just like Thomas so hilariously posted above, most picture posting is really compliment fishing. Somebody always: has something nicer, bought it cheaper, and shot a smaller group. If it didn't perform, it's just an excuse reel where it's always the equipment and not shooter. Similarly, I immediately mistrust group data or any accuracy claim who uses the magic words, "All day, if I do my part." Either they don't shoot enough or they don't understand heat transfer.
I will say that with rimfire, there can be significant deviations just with the lot number of the ammo. Even so, seeing someone shoot certain brands in smaller groups and other brands in larger groups does provide generic info about what a certain make or model of rimfire gun may like. Especially when coupled with chronograph data. That can be really helpful in debunking manufacturer's advertisements. Even so, when someone posts a lone brag group with some midrange priced ammo, I immediately have to think about how many groups they had to shoot in order to get that one brag group. Believe me, I've been there in ammo testing. I have gone out to shoot 50 groups, most of which are 1.5-3moa. Then I get one out those 50 groups that ends up being 1/2moa or less. Do I have a 1/2"moa rifle? Nope. I have an anomaly, but I could claim that I did my part