Cannot Update Image In PHP&MYSQL
===

hi guys i am working on a project where i have a student_edit.php file which updates the students
details all my data is updated successfully but there is one problem when i update lets say only two fields and not all then image is blanked and my fields updated successfully.

what i am doing is that i am showing student picture and besides it i have another input fields to browse image to update image. What i want is simple that if i am not updating image instead i update other fields image should be still there and not become blank.

Necessary code snippets is like that:

$file_name = $_FILES['picture']['name'];
	$tmp_name = $_FILES['picture']['tmp_name'];
	
	if(copy($tmp_name,"images/".$file_name)) {
		$picture = "images/".$file_name;
}
	
	
	if(!isset($_POST['picture'])) {
	
	
	$res = mysql_query("UPDATE student SET `id`='$id',`branch_id`='$branch_id',`class_id`='$class_id',`section_id`='$section_id',`roll_number`='$roll_number',`student_name`='$student_name',`father_name`='$father_name',`dob`='$dob',`student_address`='$student_address',`gender`='$gender',`status`='$status',updated=now() WHERE id='$id'") or die(mysql_error());
	
	}else {
		
		
	$res = mysql_query("UPDATE student SET `id`='$id',`branch_id`='$branch_id',`class_id`='$class_id',`section_id`='$section_id',`roll_number`='$roll_number',`student_name`='$student_name',`father_name`='$father_name',`dob`='$dob',`student_address`='$student_address',`gender`='$gender',`status`='$status',`picture`='$picture',updated=now() WHERE id='$id'") or die(mysql_error());
	
	}

                   and their is picture area where i call pics

                                <p>
				<label for="picture"><strong>Picture:</strong> </label>
                <a href="#"><img src="<?php echo $rec['picture'];?>" width="100"                 height="100" /></a>
				<input name="picture" type="file" value="">
                
			</p>

