This thread is more suited for the "
Programming Help" subforum.
As the error message says,
exif_imagetype isn't available. You'll need to use a different method. The
Fileinfo extension and (deprecated)
mime_content_type function don't currently appear to be available on the free hosts. You can use
getimagesize from the GD extension, which gets more than just the image size.
Note that
getimagesize may not detect corrupted/invalid image files. To be sure a file is really of a type, you'd need to use an image library (e.g. the aforementioned GD) to parse the file and look for errors.