When you start uploading larger images in Wordpress you have to make sure your maximum attachment size is large enough and that the execution time is not too short:
Uploading
Error
HTTP error.
[Thu May 12 16:32:25 2016] [error] [client 10.10.5.2] PHP Fatal error: Maximum execution time of 30 seconds exceeded in /httpdocs/blog/wp-includes/class-wp-image-editor-gd.php on line 182
Solution Edit p........