trying to determine which file is better.
Is the 192 file slightly better or just a transcode? I notice the blue goes a little higher on the 192 but cut off is the same.
I believe the source was unmastered
Spectograms are not a good way to determine audio quality.
They are only meaningful when there are obvious problems on the audible range.
There's no way to know what is what, and yes, one possibility (but not the only one) could be that the 192kbps is a transcode.
what are the thin blue lines in the 192 photos above 16?
The blue lines at the top of the spectrum could be the result of someone using an equalizer to attempt to remove frequency content. It looks quite similar to the other encoding.
As for the original question, spectrograms are not reliable in terms of making real comparison of quality, especially when the FFT filters used to make spectrograms can never be perfect for every use case, and always "smear" the time or frequency domains in the image, and sometimes our hearing can't tell the difference even if you can see it in a graph and vice versa. As JAZ said, spectrograms are only meaningful when there are obvious problems in the audible range. The only way to know which is better is to ABX with the original.