image dimension restrictions

File size limit is working, but I need restrictions on the dimensions of submitted images.

I tried this snippet that I found online — slightly modded by me to include max dimensions — but it isn’t working. It returns the correct randomized filename with $file['tmp_name'] in a string, but it doesn’t grab the dimensions (list($width, $height) = getimagesize( $file['tmp_name'] ); returns null), so no matter what size the image is, the result is the minimum width error on validation.

add_filter( 'wpcf7_validate_file*', 'custom_cf7_file_validation_filter', 7, 2 );
add_filter( 'wpcf7_validate_file', 'custom_cf7_file_validation_filter', 7, 2 );

function custom_cf7_file_validation_filter( $result, $tag ) {
   if ( 'test_file' == $tag->name ) {
	$name = $tag->name;
	$file = isset( $_FILES[$name] ) ? $_FILES[$name] : null;
	$minimum = array('width' => '100', 'height' => '50');
	$maximum = array('width' => '400', 'height' => '150');
	list($width, $height) = getimagesize( $file['tmp_name'] );
	if ($width < $minimum['width']) {
            $result->invalidate( $tag, "Minimum image width is {$minimum['width']}px. Your image width is $width px");
        } elseif ($height < $minimum['height']) {
            $result->invalidate( $tag, "Minimum image height is {$minimum['height']}px. Your image height is $height px");
        } elseif ($width > $maximum['width']) {
            $result->invalidate( $tag, "Maximum width is {$maximum['width']}px. Your image width is $width px");
        } elseif ($height > $maximum['height']) {
            $result->invalidate( $tag, "Maximum height is {$maximum['height']}px. Your image height is $height px");
        } 
   }
   return $result;
}

Help?