Grazie mille sei stato gentilissimo e va perfettamente,
Mi chiedevo, nel codice incollato di seguito:
if(!function_exists("generate_favicon")){function generate_favicon(){
// Create favicon.
$postvars = array(
"image" 			=> trim($_FILES["image"]["name"]),
"image_tmp"			=> $_FILES["image"]["tmp_name"],
"image_size"		=> (int)$_FILES["image"],
"image_dimensions"	=> (int)$_POST["image_dimensions"]);
$valid_exts = array("jpg","jpeg","gif","png");
$explode = explode(".",strtolower(trim($_FILES["image"]["name"])));
$ext = end($explode);
$directory = "./favicon/"; // Directory to save favicons. Include trailing slash.
$rand = rand(1000,9999);
$filename = $rand.$postvars["image"];
// Check not larger than 175kb.
if($postvars["image_size"] <= 179200){
	// Check is valid extension.
	if(in_array($ext,$valid_exts)){
		if($ext == "jpg" || $ext == "jpeg"){
			$image = imagecreatefromjpeg($postvars["image_tmp"]);
		}
		else if($ext == "gif"){
			$image = imagecreatefromgif($postvars["image_tmp"]);
		}
		else if($ext == "png"){
			$image = imagecreatefrompng($postvars["image_tmp"]);
		}
		if($image){
			list($width,$height) = getimagesize($postvars["image_tmp"]);
			$newwidth = $postvars["image_dimensions"];
			$newheight = $postvars["image_dimensions"];
			$tmp = imagecreatetruecolor($newwidth,$newheight);
				
			// Copy the image to one with the new width and height.
			imagecopyresampled($tmp,$image,0,0,0,0,$newwidth,$newheight,$width,$height);
		
			// Create image file with 100% quality.
			if(is_dir($directory)){
				if(is_writable($directory)){
					imagejpeg($tmp,$directory.$filename,100) or die('Could not make image file');
					if(file_exists($directory.$filename)){	
						// Image created, now rename it to its
						$ext_pos = strpos($rand.$postvars["image"],"." . $ext);
						$strip_ext = substr($rand.$postvars["image"],0,$ext_pos);
						// Rename image to .ico file
						rename($directory.$filename,$directory.$strip_ext.".ico");
						return '<br/><br/>
						Favicon successfully generated. <img src="'.$directory.$strip_ext.'.ico" border="0" title="Favicon  Image Preview" style="background-color:#e0e0e0" /> <a href="'.$directory.$strip_ext.'.ico" target="_blank" name="Download favicon.ico now!">Click here to download.</a>';
					} else {
						"File was not created.";
					}
				} else {
					return 'The directory: "'.$directory.'" is not writable.';
				}
			} else {
				return 'The directory: "'.$directory.'" is not valid.';
			}
		
			imagedestroy($image);
			imagedestroy($tmp);
		} else {
			return "Could not create image file.";
		}
	} else {
		return "File size too large. Max allowed file size is 175kb.";	
	}
} else {
	return "Invalid file type. You must upload an image file. (jpg, jpeg, gif, png).";	
}
}
}
Crea la favicon nelle misure 16 e 32 px come potrei dare la grandezza più grande? Tipo 64x64 ecc ? Dove devo agire?