Let's analyze the code step by step to understand the CWE-190 (Divide By Zero) vulnerability:

1. Input handling:
   - The program uses getopt() to parse command-line arguments.
   - For the 'h' option, it assigns the value of optarg to horizSubSampling using atoi().

2. Vulnerability in atoi():
   - atoi() converts a string to an integer.
   - If optarg is "0" or any non-numeric string, atoi() will return 0.

3. Usage of horizSubSampling:
   - The code doesn't show direct usage of horizSubSampling in this snippet.
   - However, horizSubSampling is likely used as a divisor in image processing operations elsewhere in the program.

4. Potential divide-by-zero:
   - If horizSubSampling is used as a divisor and its value is 0, it will cause a divide-by-zero error.

5. Lack of input validation:
   - The code doesn't check if the input for horizSubSampling is valid or non-zero.
   - This allows a user to potentially input "0" or a non-numeric value, leading to horizSubSampling being set to 0.

Conclusion:
The vulnerability arises because the code doesn't validate the input for horizSubSampling. If a user provides "0" or a non-numeric value as the argument for the 'h' option, horizSubSampling will be set to 0. When this value is later used as a divisor in calculations, it will cause a divide-by-zero error, potentially crashing the program or leading to undefined behavior. To fix this, the code should include input validation to ensure horizSubSampling is always a positive, non-zero value.