Passing PNG file request to PHP scrpt in Nginx - nginx

Question

Here is what I need to do - I need my server to serve up two versions of a set of images. The first set of images are real PNG files that sit in a folder on my server, call it /realimages. The second set of images do not actually exist. When they are requested I want to take the requested image file name e.g.
https://example.com/nosuchimage/img1.png
generate the image via the index.php script sitting inside the /nosuchmage folder (or elsewhere if easier).
That script does the following
Picks up a related image from the /realimages folder
Uses PHP GD to generate a background
Superimposes the related image on the background
serves up the result
That script has been written and is fully functional. What I do not know is how to force all PNG image requests to the /nosuchimage folder to be redirected to that script with the original request passed as a script parameterr.
I know that doing this a relatively trivial configuration issue with NGINX which involves writing a rewrite rule. However, NGINX rewriting is still quite a black art to me. Hopefully, someone here will be able to tell me just what that rewrite rule should be.

Answer 1

To redirect all the images of a certain folder, just use the code below in your configuration file.
In my case I will use the default file.
/etc/nginx/sites-available/default
location ~ \/realimages/(.+\.png)$ {
return 302 $scheme://$server_name/nosuchimage/$1;
}
// Access: http://www.example.com/images/valdeirpsr.png (Exists & Redirect to /nosuchimage/valdeirpsr.png)
// Access: http://www.example.com/images/valdeirpsr2.png (Not Exists & Redirect to /nosuchimage/valdeirpsr2.png)
To redirect only the images not found in a particular folder, just use the code below in your configuration file.
location ~ \/realimages/(.+\.png)$ {
error_page 404 $scheme://$server_name/nosuchimage/$1;
}
// Access: http://www.example.com/images/valdeirpsr.png (Exists & Show Image)
// Access: http://www.example.com/images/valdeirpsr2.png (Not Exists & Redirect to /nosuchimage/valdeirpsr2.png)