different between builds version in 1.6.37

1. There is no "Ubuntu22".
Ubuntu publishes two releases each year (in April and October), and Ubuntu release numbers have for digits with a dot (and eventually another dot number behind). I assume that you are talking about Ubuntu 22.04 (or 22.04.1) and not Ubuntu 22.10.

2. When there is no string "ubuntu" in the version number in Ubuntu, then the software source has been copied from Debian without any further Ubuntu-specific modification (which is the case here).

3. You have to be aware that compiling the same source program twice may gain different executable files, because certain information related to the compilation is stored in the executable file (e.g. version of the compiler used, eventually date and time of the compilation). That information, however, does not have any effect on the results of running the program.

4. When you look at the page https://launchpad.net/ubuntu/+source/libpng1.6/+publishinghistory you can see the history of the versions, and in https://launchpad.net/ubuntu/+source/libpng1.6/+changelog you see the full change logs.

5. One example:
Difference between version 1.6.37-3build2 and 1.6.37-3build3
"No-change rebuild to build with lto."
There is no difference in the source, but a change in compilation options (related to optimization). This will have a considerable effect on layout, size and contents of the executable file, although the behavior of the software should still be identical.

1. Ahh...yeah I forgot to name the full number, and you are right about me trying to talk about Ubuntu22.04 :D

2. The explanations are quite clear, thanks a lot for saving the day