Incoming email is missing the content

Some months ago I received an email, but the body of the email was a picture (jpg) from my computer. The sender definitely does not have the image. The content from the sender is missing, and my image is in the body of the email and as an attachment. This has happened a handful of times over the past 6-9 months, with the same image showing up in emails from various unrelated senders. I just received an email from my partner who sent me an email with a screenshot attached, but instead of receiving what he sent, I've got an email with my image that randomly shows up in my inbox. A few days ago it happened, but when I restarted my computer, the unwanted image was no longer present, and the actual email content was visible. Restarting my computer has not resolved this particular instance. Does anyone know why Thunderbird is in love with this one image of mine and why it keeps showing up in my inbox in emails from other people?