Auto image enhance for Ubuntu

If you are on the command line I recommend "convert", a command from the ImageMagick Package. Try:

$ convert -enhance -equalize -contrast image.jpg image_enhanced.jpg

And to loop a whole batch in Bash shell:

for file in *.jpg; do
 convert -enhance -equalize -contrast $file "${file%.jpg}_new.jpg"
done

Just for people that stumble over this thread and think, the results with enhance, equalize and/or contrast are ugly should definitely try this options:

convert -auto-gamma -auto-level -normalize original.jpg improved.jpg

And for the batch-lovers, having the originals in the orig-folder...:

for sp in orig/*; do 
  echo "Converting Image: $sp"
  convert -auto-gamma -auto-level -normalize $sp $(basename $sp)
done

I believe, the result is exactly what people want and need for their photos: White balance, gamma correction and overall light correction...

Have fun!

If you use the GIMP, the toolbar menu has an option for Colours->Auto->Equalize. I tried it on your "before" image and the "after" result was almost identical.

Also GIMP would give you more control over adjusting colour curves/contrast/etc. manually if you prefer.