[ImgBot] Optimize images

*Total -- 2,351.34kb -> 2,225.87kb (5.34%)

/images/source_single.jpg -- 1,517.95kb -> 1,429.70kb (5.81%)
/images/overlay.jpg -- 55.23kb -> 52.27kb (5.36%)
/images/flag.jpg -- 56.19kb -> 53.24kb (5.26%)
/images/bbox_T.jpg -- 56.78kb -> 53.86kb (5.14%)
/images/bbox_inside.jpg -- 56.73kb -> 53.83kb (5.11%)
/images/bbox_top.jpg -- 56.67kb -> 53.81kb (5.06%)
/images/cover.jpg -- 391.76kb -> 375.23kb (4.22%)
/images/bbox_multiple_flags.jpg -- 51.78kb -> 49.79kb (3.84%)
/images/bbox_multiple.jpg -- 54.01kb -> 51.94kb (3.83%)
/images/bbox_multiple_T.jpg -- 54.23kb -> 52.20kb (3.74%)

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

Author: ImgBotApp