UPDATE: This answer was given a long time ago. It will not build Raspbian Jessie - it will build whatever the Raspberry Pi Foundation's latest released image is based on. At time of writing, this is Raspbian Buster.
I am wanting to generate a custom image of Raspbian Jessie (primarily modifying the UI and adding some extra packages).
Thusfar, I have taken the image provided by the Foundation, modified it 'after the fact' and then taken a backup of the image from the SD card to then distribute. Obviously, this leaves 'fingerprints' on the image and can also makes it difficult to reproduce the steps, should it be required.
I have looked at Spindle, however it seems to have not been updated for Jessie yet. Other tools' documentation has been a bit intimidating, and have left me feeling as though there is a gap in my understanding to be able to achieve what I am trying to do.
What is the easiest way to build a custom version of Raspbian Jessie that would be considered suitable for distribution? Buildroot, Yocto project, OpenEmbedded? How does the Foundation make their image?
Tools, tutorials, documentation, etc. are all welcome - I am really looking for a point of reference to be able to work from with a bit more confidence.