Image not visible in the view or PDF

Earlier I have added a signature in the invoice (with Custom button) and it was working fine. Due to some reason it is not visible now after I upgraded to 21,
img src = “C:\Temp\Signature\Signature05.jpg” is the syntax I have used for displaying on the custom button.

anyone could through some light on why this is happening ?
It was working fine earlier

Images need web addresses not file system addresses now. Caddy2 can be used to achieve this.

it used to work earlier, but what is the reason or advantage of this change ?

It never worked for all operating systems.