Imagick View the Output

Hi E's, The code in snippet code put a watermark in a image, the problem is I can't see the picture when I execute the script:
in practice:
File index.php contain the code in snippet code.
For I see the picture created by index.php script I create the file mostra.php with this contain
=====================
<img src="index.php" />
=====================
When I execute the file mostra.php, the browser don't show the picture, don't show anything.

What I do wrong?
What is the best way to see the result of index.php?

Regards, JC

<?php
/* Create Imagick object */
$im = new Imagick( 'imagem.jpg' );
/* Create a drawing object and set the font size */
$draw = new ImagickDraw();
$draw->setFontSize( 30 );    
/* Make the watermark semi-transparent */
$draw->setFillAlpha( 0.4 );
/* Set gravity to the center. More about gravity: 
http://www.imagemagick.org/Usage/annotating/#gravity */
$draw->setGravity( Imagick::GRAVITY_CENTER );
/* Write the text on the image
Position x0,y0 (Because gravity is set to center)
Rotation 45 degrees.
*/
$im->annotateImage( $draw, 0, 0, 45, "Copyright" );
/* Output */
header( "Content-Type: image/{$im->getImageFormat()}" );
echo $im;
?>

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