You can not use getimagesize() on a direct URL you must point to the image path local to the server. According to the error it's passing the following direct url - http://dev.foobar/wp-content/uploads/2015/11/subheader-image-jobline-1.jpg - to the function as opposed to the path.
If thisI'm assuming WP is a theme you are working on andinstalled locally, did you are using image attachments use the get_attached_file() filemake sure to returnedit your image path so you can properly pass it through getimagesize()hosts file. Example:
127.0.0.1 dev.foobar