Image upload system.

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<?php//define a maxim size for the uploaded images in Kb define ("MAX_SIZE","99999999999999999"); //This function reads the extension of the file. It is used to determine if the// file  is an image by checking the extension. function getExtension($str) {         $i = strrpos($str,".");         if (!$i) { return ""; }         $l = strlen($str) - $i;         $ext = substr($str,$i+1,$l);         return $ext; }//This variable is used as a flag. The value is initialized with 0 (meaning no // error  found)  //and it will be changed to 1 if an errro occures.  //If the error occures the file will not be uploaded. $errors=0;//checks if the form has been submitted if(isset($_POST['Submit']))  { 	//reads the name of the file the user submitted for uploading 	$image=$_FILES['image']['name']; 	//if it is not empty 	if ($image)  	{ 	//get the original name of the file from the clients machine 		$filename = stripslashes($_FILES['image']['name']); 	//get the extension of the file in a lower case format  		$extension = getExtension($filename); 		$extension = strtolower($extension); 	//if it is not a known extension, we will suppose it is an error and         // will not  upload the file,  	//otherwise we will do more tests if (($extension != "jpg") && ($extension != "jpeg") && ($extension != "png") && ($extension != "gif"))  		{		//print error message 			echo '<h1>Unknown extension!</h1>'; 			$errors=1; 		} 		else 		{//get the size of the image in bytes //$_FILES['image']['tmp_name'] is the temporary filename of the file //in which the uploaded file was stored on the server $size=filesize($_FILES['image']['tmp_name']);//compare the size with the maxim size we defined and print error if biggerif ($size > MAX_SIZE*1024){	echo '<h1>You have exceeded the size limit!</h1>';	$errors=1;}//we will give an unique name, for example the time in unix time format$image_name=time().'.'.$extension;//the new name will be containing the full path where will be stored (images //folder)$newname="images/".$image_name;//we verify if the image has been uploaded, and print error instead$copied = copy($_FILES['image']['tmp_name'], $newname);if (!$copied) {	echo '<h1>Copy unsuccessfull!</h1>';	$errors=1;}}}}//If no errors registred, print the success message if(isset($_POST['Submit']) && !$errors)  { 	echo "<h1>File Uploaded Successfully! Try again!</h1>"; } ?> <!--next comes the form, you must set the enctype to "multipart/frm-data" and use an input type "file" --> <form name="newad" method="post" enctype="multipart/form-data"  action=""> <table> 	<tr><td><input type="file" name="image"></td></tr> 	<tr><td><input name="Submit" type="submit" value="Upload image">       </td></tr> </table>	 </form>