Photo not Valid?

I'm trying to add a new model (which I've done countless times, I've been on here a couple years now), and it won't let me. It keeps telling me that the image isn't valid. I don't know what that means. I'm doing it the same way I've always done it, and it's not too big.

Here's exactly what's coming up in red at the top of the page: Image (horse image) file must be a valid image.

This is happening to me too as I try to add some new photos I took today, just now.

*Occasionally* I've had where I tried to save a file too fast or something and it didn't save properly and I get this message, but this is happening with every photo, and I was able to post one to social media as an experiment.

They are all .jpg

So it's something with the site, I think.

I started seeing this message this afternoon when I tried to replace a photo of an existing model.