Mail signature - missing plug-in message when adding photo
My MacBook Pro Mid-2012, 13-inch, running macOS Sonoma 14.1.1, has some issues involving Apple Mail. I have a signature and I want to add in a PNG file into my signature as a logo. However, I have tried searching it up on the web, double-clicking and then clicking 'copy image address', but it doesn't work. I've tried dragging it straight from the web to the signature editing box, I've tried dragging the image from the web to my desktop and then importing to Mail from there, I've even tried copying the image address and pasting it in as a 'URL'.
However, each time I try, the image inserts and then it shows 'Missing plug-in.' I read some other posts about similar situations and many users had just upgraded to macOS Sierra. However, I'm running Sonoma and that should have nothing to do with Sierra. I've tried terminal commands, restarting, the usual, but nothing (good) happens.
This is the image, if it helps.
This situation is really frustrating and I've wasted an entire afternoon looking at posts about this. Please help.
[Edited by Moderator]
MacBook Pro 13″, macOS 14.1