After upgrading to WordPress 4.5.1 I wasn’t able to upload images anymore. Neither from the iPad nor from my Macbook. It seems to be related to Imagick and the image size you’re trying to upload. While there is no update for WordPress yet, a small addition to the functions.php of your current theme will fix it temporally:

add_filter( 'wp_image_editors', 'change_graphic_lib' );

function change_graphic_lib($array) {
return array( 'WP_Image_Editor_GD', 'WP_Image_Editor_Imagick' );
}