GD: Transparency to a gif (from mask?)

[Accipiter]

Hi all,

I am trying to create automatically generated avatars.
The user uploads an image, and then I copy my "foreground" on top of it (in shape of a wreath).
So.. What I have is a truecolor resource in a specific width and height

But as I use imagegif() to send it, I want the "background" colored pixels to be transparent.
Example of how it looks now:
[url=http://www.thesodality.org/test.php]http://www.thesodality.org/test.php[/url]

The [color=blue]blue[/color] is the user image, the entirely brown ones (not the ones antialiasing the green leaves) should be transparent.
My two options are:
1) Using a black and white mask image. This way I won't risk making any pixels within the user image transparent.
2) Setting the brown color to transparent. If the users image contains the exact same brown, it will get holes :P

Unfortunately, I have failed to succeed with any of the two.

Help is highly appreciated!

/Accipiter

Ps. If you want to see how I've done it:

[code]
// $thumb is the user uploaded image, resized to the same width and height as the overlay.

$overlay = imagecreatefrompng($overlay_image_path);
imagealphablending($overlay, true);
imagecopy($thumb, $overlay, 0,0,0,0, $width, $height);

// This part fails!
$image = imagecreatetruecolor($width, $height);
$transparent = imagecolorallocate($image, 223,192,137); // Those numbers are the brown color
imagecolortransparent($image, $transparent);

imagecopy($image, $thumb, 0,0,0,0, $width, $height);


header ("Content-Type: image/gif");

imagegif($image);[/code]

[Accipiter]

I finally succeeded.
If anyone else needs to set a selected part transparent, this is one way:

[code]// $thumb is the user uploaded image, resized to the same width and height as the overlay.

// Adding the overlay image upon the users pictures
$overlay = imagecreatefrompng($overlay_image_path);
imagealphablending($overlay, true);
imagecopy($thumb, $overlay, 0,0,0,0, $width, $height);

// Reducing the colors to 255 (not 256. I want the last one available)
imagetruecolortopalette ($thumb, false, 255);

$r = $g = $b = 0;
// Finding a unique, unused color
while( imagecolorexact($thumb, $r, $g, $b) != -1 )
{
if( $r <= $g )
$r++;
elseif( $g <= $b)
$g++;
else
$b++;
}

imagecolorset ( $thumb, 255, $r, $g, $b );  // Set the last, unused index, to our unused color

// The mask is a Black&White image with the White set to transparent.
$mask = imagecreatefromgif($mask_image_path);
$imaskbg = imagecolorexact ( $mask, 0,0,0 );  // Get the palette index of the black color
imagecolorset( $mask, $imaskbg, $r, $g, $b );  // Change the black color to our unused color

imagecopy( $thumb, $mask, 0,0,0,0,$width, $height); // Copy it over. The white will be transparent.
imagecolortransparent($thumb, 255);  // Set our color to transparent.

header ("Content-Type: image/gif'");
imagegif($thumb);[/code]

It worked for me atleast :)

[Accipiter]

(One last question. How do I set a topic as Solved?)