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 php.ini to increase the maximum_execution_time variable to 80 seconds
vi /etc/php.ini
max_execution_time = 80
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