How to allow new images extension as JPEG 2000

I have a blog running with Ghost (2.21.1). When I do some test with the google page speed insights, they say that I can imporve my site by putting images with jpeg 2000 instead of jpeg. But when I try to add a jpeg2000 in a article thumbtail, I have an error : wrong format. So how can I upload jpeg 2000 ?

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