Troubleshooting adding a JPG to my iCloud email signature on PC

I'm trying to add a JPG image to my iCloud email signature. I've been able to add a text signature (settings > all settings > composing > add a signature) but there's no button to attach an image. I've tried adding it as a PNG and PDF, dragging and dropping the file, and copying and pasting it (both through a right click and keyboard commands) but nothing's working. I'm also accessing iCloud Mail through Chrome on a PC as well. Thanks in advance for your help!