#the original blob is in $blobdata - if I print it out here
# then I can see it's fine (exists, looks right).

#in the following line I've tried jpeg,jpg,JPG
my $image=Image::Magick->new(magick=>'JPEG');
$image->BlobToImage($blobdata);

my $newblob = $image -> ImageToBlob() ;
print $newblob; 
#at this point, $newblob appears to be empty