Block high-resolution JPGs being uploaded to the Wordpress Media Library

functions.php

//
// Block high-res JPGs (e.g., direct photos direct from the camera) being uploaded to the Wordpress Media Library
//
// Add this to the themes functions.php file - If an image is a JPG larger than 500kb then we block it but also alert the
// user if the image is higher than 96dpi.
// The file may be uploaded regardless if the file size is smaller than 500kb.
//
function ingeni_media_library_upload_filter( $file ) {
	$is_allowed = true;

	// Limit file sizes to 500k for JPGs
	$max_jpg_size = 500;
  
	// Limit DPI
	$max_dpi = 96;
	$preferred_dpi = 72;
  
	// Limit x or y dimensions
	$max_dimension = 4000;


	// Let's put some limit around uploaded JPGs - no photos direct from the camera allowed.
	if ( ( $file['size'] > ( $max_jpg_size * 1024 ) ) && ( $file['type'] == 'image/jpeg' ) ) {
		// The file is > 500k
		$is_allowed = false;
		$file['error'] = 'JPG images must be smaller than '.$max_jpg_size.'k';

		// Grab the EXIF data
		$exif = exif_read_data( $file['tmp_name'], 'IFD0');

		// Only check the X resolution for DPI
		if ( array_key_exists('XResolution', $exif) ) {
			
			$x_dpi =  $exif['XResolution'];
			if ( !is_numeric( $x_dpi ) ) {
				$x_dpi = floatval( $x_dpi );
			}
			$x_dpi = intval( $x_dpi );

			if ( $x_dpi > $max_dpi ) {
				$is_allowed = false;
				$file['error'] = 'This is a high resolution image ['.$x_dpi.'dpi]. It must be reduced to '.$preferred_dpi.'dpi using an image editor like PhotoShop or Paint.NET';
			}
		}
	}
    return $file;
}
add_filter('wp_handle_upload_prefilter', 'ingeni_media_library_upload_filter' );