ImageSecure Class is download from :
https://mega.nz/file/06IWzKga#oOyAoL2ALXxi2odwkxsVkcTtWgik4XNR-4yL3XLR4W4
(from https://stackoverflow.com/questions/38509334/full-secure-image-upload-script)
All the images generated by ImageSecure Class will be displayed through a phtml file, so that you can do hotlink protection for this file extension