How do you upload a signature image?

In the profile section, it says for your signature image that you have to give the website address like https: //www. etc.,etc., for the image/picture. But, when I do that, it says it's too big/ has too many bytes (more than 30 kbytes). Then when I click on other people's signature pictures, they are just .jpg images from their computer files, not an online http address.

OK, I know this is a pain-in-the-arse post, but if someone feels charitable, I'd appreciate help in posting a signature image in my profile.