@ndnhc I think 2nd image is releated to the exchanges name which is 5 chars.
So My guess is CATGBEXCB
I've already told "BCTGBEXAC" (whose first and last 2 letters were found by your way).
My observation is that two already known images have given just 2 letters each.
It is more likely that the clue will have around 6 letters. That is the second image will give around 2 letters.
Since all the letters known till now are a. b or c, which could be hexadecimal digits.
I think the second image will reveal 3 characters, and when we convert it to decimal we will get a
9 digit code. all numbers.