Commands used:
```
find . -type f -iname "*.png" -exec advpng -z4 {} \;
find . -type f -iname "*.png" -exec optipng -o7 -preserve {} \;
find . -type f -iname "*.png" -exec pngcrush -rem allb -brute -reduce -ow {} \;
```
Commands used:
```
find . -type f -iname "*.png" -exec advpng -z4 {} \;
find . -type f -iname "*.png" -exec optipng -o7 -preserve {} \;
find . -type f -iname "*.png" -exec pngcrush -rem allb -brute -reduce -ow {} \;
```