AllSync & AllDup

He calls that the "reference file".
And for similar picture / similar audio searches, that is the file that is "designated" as 100%, & as such, upon which other files are percentage (%) matched against.

That said, I don't know that there is a particular meaning to which file is marked as the ...

After running AllDup on a massive amount of photos (>138K), as expected, I received a massive amount of duplicates. My query is.... what is the significance of the one yellow/gold line? Is AllDup determining that this photo is the original or best quality? I have attached a screen shot for reference ...