You can use Boxoft Batch Photo Processor to brighten pictures. it also allows you to adjust image saturation, contrast, color balance, sharp, etc. it provide other 4 kinds of function, such as "Annotate", "Transform", "Touch-up","Effects", etc. choose one depend on your requirement.
More details follow steps below:
Launch it by double clicking its desktop icon, add some aim pictures;
On the left-right box, click "Touch-up", choose "Brightness";
According to prompt, click green arrows towards the right to start editing picture;
On pop-up box, you can adjust "Brightness" or "Saturation" by dragging bar, by your hand, picture turn bright or dark, if you adjust saturation, the picture color displays vividly or flatly;