[ImgBot] Optimize images

*Total -- 142.56kb -> 121.51kb (14.76%)

/screenshots/comparison.png -- 38.32kb -> 30.83kb (19.54%)
/screenshots/scnn.png -- 92.26kb -> 78.86kb (14.53%)
/data/test_data/tiger.jpeg -- 11.98kb -> 11.83kb (1.28%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp