If you want to draw a rectangle with rounded corners, you can use this simple function...
Rectangle starts at x1y1 and ends at x2y2. $radius defines radius of circled corner.
<?
function ImageRectangleWithRoundedCorners(&$im, $x1, $y1, $x2, $y2, $radius, $color) {
// draw rectangle without corners
imagefilledrectangle($im, $x1+$radius, $y1, $x2-$radius, $y2, $color);
imagefilledrectangle($im, $x1, $y1+$radius, $x2, $y2-$radius, $color);
// draw circled corners
imagefilledellipse($im, $x1+$radius, $y1+$radius, $radius*2, $radius*2, $color);
imagefilledellipse($im, $x2-$radius, $y1+$radius, $radius*2, $radius*2, $color);
imagefilledellipse($im, $x1+$radius, $y2-$radius, $radius*2, $radius*2, $color);
imagefilledellipse($im, $x2-$radius, $y2-$radius, $radius*2, $radius*2, $color);
}
?>