Array to string conversion in CodeIgniter while resizing
Based on the doc here...
https://ellislab.com/codeigniter/user-guide/helpers/directory_helper.html
Looks like $val in your loop could be an array sometimes, representing a subdirectory (e.g., you have thumbs within public/img/pics). You may want to limit your directory_map to only 1 level:
$AllImages = directory_map($dir, 1);