check image size for uploading

gistfile1.txt

// check for file upload size //
add_action( 'admin_init', 'wpse_28359_block_vendors_from_uploading_small_images' );

function wpse_28359_block_vendors_from_uploading_small_images()
{
    if( !current_user_can( 'administrator') )
        add_filter( 'wp_handle_upload_prefilter', 'wpse_28359_block_small_images_upload' ); 
}

function wpse_28359_block_small_images_upload( $file )
{
    // Mime type with dimensions, check to exit earlier
    $mimes = array( 'image/jpeg', 'image/png', 'image/gif' );

    if( !in_array( $file['type'], $mimes ) )
        return $file;

    $img = getimagesize( $file['tmp_name'] );
    $minimum = array( 'width' => 800, 'height' => 450 );

    if ( $img[0] < $minimum['width'] )
        $file['error'] = 
            'Image too small. Minimum width is ' 
            . $minimum['width'] 
            . 'px. Uploaded image width is ' 
            . $img[0] . 'px';

    elseif ( $img[1] < $minimum['height'] )
        $file['error'] = 
            'Image too small. Minimum height is ' 
            . $minimum['height'] 
            . 'px. Uploaded image height is ' 
            . $img[1] . 'px';
			$img = getimagesize( $file['tmp_name'] );
    $minimum = array( 'width' => 800, 'height' => 450 );
	
	if( !in_array( $file['type'], $mimes ) )
        return $file;

    $img = getimagesize( $file['tmp_name'] );
    $maximum = array( 'width' => 800, 'height' => 450 );

    return $file;
}