Question

I have been tasked with a problem where i need to pickup one image froma set of 1000 and serve it to the user based on the parameters passed in the get query.
This was simple.
Adiditonally, i have been asked to serve the image in such a way that even if the same file is server everytime, the sha1 hash of the image file should come different.

To achieve this,We could just add random pixels in the image background at random places.

Can somebody tell me how i can acheive this using the GD library

Answer 1

Use Imagesetpixel.

$img = imagecreatefrompng('your_image.png');
$red = imagecolorallocate($img, 255, 0, 0); 
imagesetpixel($img, $x, $y, $red);
........
........

On the other hand why would you want to change the sha1 hash of the image on every request?

Edit: Since you want a transparent pixel, you are going to need imagealphablending and something like this:

$img = imagecreatefrompng('your_image.png');
imagealphablending($img, false);
$transparent = imagecolorallocatealpha($img, 255, 255, 255, 127);
imagesetpixel($img, $x, $y, $transparent);
imagesavealpha($img, true);         
imagepng($img, 'my_saved_file.png');