What's wrong with doing it client side instead of making the json encoder do mime sniffing on the data?

img.src = 'data:image/png;base64,' + data.Blob;

@OneOfOne There's nothing wrong with sniffing in a browser scenario but I'm targeting another class of applications where there is no room for such measures: https://cyberphone.github.io/openkeystore/resources/docs/jsonsignatures.html

Yes, an option must also work for unmarshalling.

It's rather trivial to implement your own type for that though.

https://play.golang.org/p/FYFtvrdWnq

@OneOfOne Indeed I could but you should consider this issue related to a bunch of issues which makes the current Marshaller/Unmarshaller close to useless in my context:
#14750
#14749
#14135