Transparent Pixel Response
This package provides a modified Response class, which returns the image in GIF format of size 1 by 1 pixel. Frequently this image is used when registering openings of e-mail messages.
I used the example from article Transparent pixel response with Symfony, how to track email opening.
composer require gander/symfony-transparent-pixel-response
The Transparent Pixel Response is open-sourced software licensed under the MIT license