Refactor:Improve the logic so that it does not decode base 64 for the test image each time (#9264)
### What problem does this PR solve?
Improve the logic so that it does not decode base 64 for the test image
each time
### Type of change
- [x] Refactoring
- [x] Performance Improvement
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Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>