Set up crop borders using green arrows. Each arrow sets border fromone side (top, bottom, left and right). You can use double arrow for moving top and bottom arrow or left and right arrow at same time - this will preserve width and height of cropping area.
You can set up perspective and handle it with the yellow panel. Click reload default for normal perspective.
How to edit perspective? Click into the image and drag yellow rectangle as you want. Then click Edit perspective Button. If you're not satisfied with the result, repair the yellow rectangle and click the button again.
When the checkbox "Apply perspective when loading next image" is checked, the change of perspective will be applied at next loaded image.
You can set up brightness and contrast.
Quality means quality of compression of JPEG - from 60 (lower quality, low size in MB) to 100 (best quality, high size in MB).
This will crop all the images in query with your settings. It's simply batch processing.
If you're not satisfied with the result, simply double click on the image in listbox. This image will be loaded again and when you crop it, the result will be overwritten.
Your images are not overwritten. Results are saved into the folder Files in the root folder of your images. You can open last cropped image by clicking blue label or open whole folder.