I'm using the twentythirteen theme and trying to get the header to adapt to screen resolution.
I've uploaded several image files with the required resolutions, and changed my custom-header.php source code according to what is suggested here.
The website, www.ensemblepourviroflay.org/wp/ (can't link more than twice with newbie account), does not seem to be displaying any of the images, at whichever resolution. I have pasted the content of my custom-header.php file here.
I would appreciate it if a kind stranger would have a look.