Thread: Removing add_image_size() presets

// setup different image sizes
if ( function_exists( 'add_image_size' ) ) {
	add_image_size('blog-thumbnail', 150, 150); // blog post thumbnail size, box crop mode
	add_image_size('sidebar-thumbnail', 50, 50, true); // sidebar blog thumbnail size, box crop mode

	// create special sizes for the ads
	add_image_size('ad-thumb', 75, 75, true);
	add_image_size('ad-small', 100, 100, true);
	add_image_size('ad-medium', 250, 250, true);
	//add_image_size('ad-large', 500, 500);
}

function sgr_filter_image_sizes( $sizes) {
		
	unset( $sizes['thumbnail']);
	unset( $sizes['medium']);
	unset( $sizes['large']);
	unset( $sizes['blog-thumbnail']);
	unset( $sizes['sidebar-thumbnail']);
	unset( $sizes['ad-thumb']);
	unset( $sizes['ad-small']);
	unset( $sizes['ad-medium']);
		
	return $sizes;
}
add_filter('intermediate_image_sizes_advanced', 'sgr_filter_image_sizes');