You will have to download the image to a tmp location and set the tmp_name
to that location. You can use file_get_contents
from php or HttpSocket
from cake.
You will need to avoid using the usual php is_uploaded
checks as the file would not have been uploaded.
You will want to add a bit more security to make sure people dont put scripts or other things for uploading as that can be a security issue.
example using HttpSocket. After the upload is done you could do $Download->file->path()
to get its location.