<?php
if($_POST){
foreach ($_POST['resim'] as $value) {
$resim_array.=$value.'@';    
}
echo substr($resim_array,0,-1);
}
?>



<form action="" method="POST">

<input type="checkbox" name="resim[1]" value="1.jpg" />
<input type="checkbox" name="resim[2]" value="2.jpg" />
<input type="checkbox" name="resim[3]" value="3.jpg" />
<input type="checkbox" name="resim[4]" value="4.jpg" />
<input type="checkbox" name="resim[5]" value="5.jpg" />

<input type="submit" value="GÖNDER" />

</form>