Looks like rust, but I still wouldn’t eat them.

It’s the salt in the brine. You can prevent it by putting plastic wrap over the mouth before you put the lid on.

Rust or mold, it doesn’t really matter. As other have said it’s on the outer part of the circle - the bit contacting the outer glass thread. The inner circle is the plug that contacts the contents and is clear.

If it feels scratch with a finger nail its rust, if it’s soft and scrapes off its mold. But as I said it’s not in contact with the contents so it doesn’t matter.

Also the contents of the jar are pickled. That means brine or vinegar, which is highly acidic and is what keeps the food fresh/prevents mould and bacteria. So if the pickles themselves look fine then they’ll be fine to eat. If the pickling had failed the contents would be mouldy.

Rust would make sense as the content of the jar is acidic and acids accelerate rust. There could be small pockets of air left at that location when you seal the jar and some fluid inevitably gets forced out as it is sealed; air plus acid is perfect for rust. But the jars internally themselves were otherwise well sealed as there is no rust in the inner bit of the circle, suggesting it plugged the jar contacting the fluid directly and no gas was left.

This likely reflects the jar lids are not quite perfect for the jar or possibly not screwed on to their perfect max tightness leaving air behind at those locations. But they were screwed on well enough to seal the content.

I make a lot of jam and am very careful to sterilise the jars beforehand - wash thoroughly, heat in the oven, dry with clean cloth. Lids with that seal strip are trickier, so after washing and drying, I line them up, pour white vinegar into each, and leave them half an hour. Dry off with paper towels. That way I never get mould on the seal.

I’m guessing you didn’t do any of that? The pickles are possibly all right, but… it’s a risk I wouldn’t take. And I’m still getting through a batch of spicy plum sauce I made in 2015! Never had any mould on it.

If shit ever truly hits the fan, some y’all are going to starve.

I don’t care if it’s rust or mold. Either way is harmless. Wipe it with your finger and you will know instantly. Almost 100% it’s rust, which happens when you combine salt and iron.

If anyone thinks I’m an idiot, consider the salinity and pH. Nothing is growing in there, nothing can grow in there. I’ve got homemade hot sauce that is several years old, between the acidity and salt, it can’t go bad.

Are these re-used lids?

It’s clearly mold (e okay technically it’s mildew), and people who say it’s rust are smoking the drapes.

But it’s safe to eat the pickles because they’re not contaminated.