You can use ImageMagick with the auto-level or level flags.

convert input.jpg -auto-level output.jpg
convert input.jpg -level 1%,99% output.jpg

On Linux or Mac, you can use a bash control structure to perform the operation on multiple image files.

for f in *.jpg ; do
   convert "$f" -level 1%,99% "${f%.jpg}-level.jpg"
done

I don't know the equivalent command for Windows. Anyone who knows, feel free to edit to add.

You can use ImageMagick with the auto-level or level flags.

convert input.jpg -auto-level output.jpg
convert input.jpg -level 1%,99% output.jpg

On Linux or Mac, you can use a bash control structure to perform the operation on multiple image files.

for f in *.jpg ; do
   convert "$f" -level 1%,99% "${f%.jpg}-level.jpg"
done

For Windows, you can install a bash shell, like Cygwin or Windows Subsystem for Linux.

Anyone who knows the native cmd or PowerShell commands for Windows, feel free to edit to add.