What should you pay attention to when dynamically generating images in GIF format for adults?

If you use
int imagecreatefromgif(string filename);
to take out a GIF format graphic and use it as a background or basic canvas sample to draw graphics on it, please note:
If there is no pigment in this file, you will not be able to use.
Solution, you can use
int imagecreate(int x_size, int y_size);
Create a completely empty graphic. Draw graphics on it. Use black as the transparent color.
This newly created graphic should be the same size and absolute position as the original graphic. Just place it above the original graphic.

Original graphic file

Completely empty file photo.php
photo.php code:
Header("Content-type: image/gif");
$im = imagecreate(200,300);
$black = ImageColorAllocate( $im, 0,0,0);
$red = ImageColorAllocate($im, 255,0,0);
$blue = ImageColorAllocate($im, 0,0,255);
imagerectangle($im,100,200,150,200,$red );
imagestring($im,2,120,150,"aaaaaaaa",$blue);
imagecolortransparent($im,$black);
//Use black as a transparent color
ImageGif($im);
ImageDestroy($im);
?>
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The above introduces the adult gif. What should we pay attention to when dynamically generating images in gif format? , including adult gif content, I hope it will be helpful to friends who are interested in PHP tutorials.