Note: By default DOWO Digital only enable GD, and not Imagick. This guide is only relevant if you ahve enabled Imagick.
Some Wordpress installs will display HTTP Errors when uploading and crunching images. This occurs when Wordpress uses Imagick to convert and process the images. Imagick is quite a resource intensive application, and runs into the memory limits for all standard accounts (no more than 512MB RAM at once per account).
To resolve you shoul tell Wordpress to revert to using GD instead. To do this open wp-includes/class-wp-image-editor-imagick.php, and change line 76 to return false (rather than return true).
