It is quite easy to create a 1 pixel white or transparent image file…
Thanks, but already known. The pixel trick in an email tells the sender you've viewed the email, and that the address is live (among the thousands of ones they send out that bounce because they don't exist).
As I'm sure you know, when you open an email and you have your email client set to load images automatically, the pixel is retrieved from the remote server it's on in order to display the "image" in the email. That server picks up the email address it was sent to. From there, your address gets added to a list of verified emails so it can be used to spoof more spam, get more spam sent to you, and so on. It's why you should never have your email client set to load images automatically.
But, the pixel itself is just a 1x1 raster image pixel you can create with any raster image editor (Photoshop, Preview, Acorn, etc.). There isn't a single thing about it that's "unique".