Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

We're making progress. No one is contesting that this is really how it looks on history-matters:

So now the only question is: what is it? Is the mark a "spot" that is, a spontaneous rendering that occurred by accident? That is a huge claim. We've all been taking and looking at photos our whole lives. Go ahead and take out your family albums. How many of the photos have marks like that? None, you say? Well, then what basis is there to claim that is what it is here? 

The burden of proof is on the one who is making the claim. Let's see them come up with a single photo from the entire world wide web that has a similar mark as this which occurred spontaneously by accident. I don't think they can find such a thing. 

Remember what I said: that anybody can claim anything. But, to claim that this is an accidental defilement of the photo when we know from our own experience that such accidents are exceedingly rare, makes is non-credible. Photos get defiled. But usually, someone spills coffee on it or an alcoholic beverage or something like that. But, we are talking about an ink-mark here. And, it couldn't occur by accident from someone holding a pen because, invariably, the mark would be larger. It could never be that small. There is too much leverage involved. If you flick your wrist when you're holding a pen, the tip of the pen is going to travel. 

But, let's bottom line this: they have not provided any examples of known accidental renderings that look like this. And actually, they haven't provided any renderings at all. And that means the claim is categorically rejected as worthless. 

This is an inkspot on a photograph, and there is no reason to think it occurred by accident. And knowing that Lovelady took an ink pen to the photograph, after the other arrow was drawn a month before, it makes it highly likely that Lovelady did it. 

That's the default. I don't make the rules. I just enforce them.