How I can know that a Ubuntu ISO was created using a Live CD customization tool?

How I can know that a Ubuntu ISO was created using a Live CD customization tool, e.g. remastersys? Or how I can know that a Ubuntu ISO was created or generated?
Do Live CD customization tools leave things in generated ISO?

I'd suggest checking the SHA256 sum for the .iso you have vs the official ones.

1. Download the SHA256SUMS file from the respective release page here: http://releases.ubuntu.com/




2. Ensure that the iso you want to verify matches the file name of the iso you believe it could be from (one of the filenames in SHA256SUMS).




3. Ensure that the downloaded SHA256SUMS file and the iso are in the same folder.




4. Execute these commands in a terminal:

   
   
   

   cd 
   sha256sum -c ./SHA256SUMS | grep OK
   



5. If it prints the file name then OK, it is an official iso otherwise it has been changed.