[Theme Hemingway] Function disappeared!

Hi guys,

I really need your help.
I just created a child theme for my theme. Everything’s okay except the fact that at least one function has disappeared. I can not figure out why, but with my child theme I’m not able to edit the header image on my site. (Normally it should be possible by simply clicking the “Edit” button on my WP).

Has anybody a solution for this?

=> http://matthieudaubinphotographie.fr/

Thank you very much.