Thank you so much ...
I'm trying to do that right now but I'm using 3rd party (Highcharts) to auto create graph to png into our server.
I also noticed their generated image file name is chart.238efb83bfef4r8ff8.png .
Still finding a way to override that auto-created file name structure and omit the first 6 characters.
Hopefully this is the right solution.
Will let you know. Thank you for prompt reply.