ahamelers

Okay, thanks! I think I was treating this as bug reporting, rather than support. Oops.

I am having the same problem. It seems like a bug, looking at the error messages I’m getting in my logs:

[Tue Feb 10 11:13:34 2015] [error] [client 128.175.82.107] PHP Warning:  imagecreatetruecolor(): Invalid image dimensions in /home/www/html/library/wp-includes/media.php on line 2043, referer: [...]/wp-admin/customize.php?theme=[..]
[Tue Feb 10 11:13:34 2015] [error] [client 128.175.82.107] PHP Warning:  imageantialias() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 283, referer: [...]/wp-admin/customize.php?theme=[...]
[Tue Feb 10 11:13:34 2015] [error] [client 128.175.82.107] PHP Warning:  imagecopyresampled() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 285, referer: [...]/wp-admin/customize.php?theme=[...]
[Tue Feb 10 11:20:28 2015] [error] [client 128.175.82.107] PHP Warning:  imagecreatetruecolor(): Invalid image dimensions in /home/www/html/library/wp-includes/media.php on line 2043, referer: [...]/wp-admin/customize.php?theme=[...]
[Tue Feb 10 11:20:28 2015] [error] [client 128.175.82.107] PHP Warning:  imageantialias() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 283, referer: [...]/wp-admin/customize.php?theme=[...]
[Tue Feb 10 11:20:28 2015] [error] [client 128.175.82.107] PHP Warning:  imagecopyresampled() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 285, referer: [...]/wp-admin/customize.php?theme=[...]
[Tue Feb 10 14:20:34 2015] [error] [client 128.175.82.107] PHP Warning:  imagecreatetruecolor(): Invalid image dimensions in /home/www/html/library/wp-includes/media.php on line 2043, referer: [...]/wp-admin/customize.php?return=%2Fdisc%2Fwp-admin%2Fthemes.php&autofocus[control]=header_image
[Tue Feb 10 14:20:34 2015] [error] [client 128.175.82.107] PHP Warning:  imageantialias() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 283, referer: [...]/wp-admin/customize.php?return=%2Fdisc%2Fwp-admin%2Fthemes.php&autofocus[control]=header_image
[Tue Feb 10 14:20:34 2015] [error] [client 128.175.82.107] PHP Warning:  imagecopyresampled() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 285, referer: [...]/wp-admin/customize.php?return=%2Fdisc%2Fwp-admin%2Fthemes.php&autofocus[control]=header_image
[Tue Feb 10 14:23:25 2015] [error] [client 128.175.250.132] Invalid URI in request GET  HTTP/1.1
[Tue Feb 10 14:32:58 2015] [error] [client 128.175.82.106] PHP Warning:  imagecreatetruecolor(): Invalid image dimensions in /home/www/html/library/wp-includes/media.php on line 2043, referer: [...]/wp-admin/customize.php?return=%2Fdisc%2Fwp-admin%2F&autofocus[control]=header_image
[Tue Feb 10 14:32:58 2015] [error] [client 128.175.82.106] PHP Warning:  imageantialias() expects parameter 1 to be resource, boolean given in /home/www/html/library/wp-includes/class-wp-image-editor-gd.php on line 283, referer: [...]/wp-admin/customize.php?return=%2Fdisc%2Fwp-admin%2F&autofocus[control]=header_image
[Tue Feb 10 14:32:58 2015] [error] [client 128.175.82.106] PHP Warning:  imagecopyresampled() expects parameter 1 to be resource, boolean given in [..]/wp-includes/class-wp-image-editor-gd.php on line 285, referer: [..]/wp-admin/customize.php?return=%2Fdisc%2Fwp-admin%2F&autofocus[control]=header_image

After searching for a while for this for myself, and almost making a bug ticket, I found this: https://core.trac.www.ads-software.com/ticket/17242#comment:53

You have to add the argument ‘max-width’ and some huge number. Here’s mine:

$args = array(
   'default-image' => get_template_directory_uri() . '/images/headimage.jpg',
   'random-default' => true,
   'height'        => 350,
   'flex-width'   => true,
   'max-width' => 4000,
   'header-text'  => false,
   'uploads'       => true,
);
add_theme_support( 'custom-header', $args );

No idea why that argument is missing from the codex.