If you use the google charts qr code generator you get html output that looks like this
<img src="https://chart.googleapis.com/chartcht=qr&chs=500x500&=Hello+world&choe=UTF-8">`
To me that does not look look like a data URI and it has no filename extension either.
What kind of image format is this?
PNG. It doesn't have the .png
file extension, but it does have the image/png
MIME type:
When loading the image, the browser receives the following header:
content-type:image/png
This is what lets the browser know that it's a PNG.