Implement a simple checkbox to Settings Pane or elsewhere!

Hello!

The subject is as is!

I need to implement a checkbox into the Settings Pane, which result I would like to have in the plugins. For example, I have a watermark-plugin. And it's included in the config.php as it should. Therefore, sometimes I need to upload images without being watermarked. For this reason I want to place a checkbox, instead of switching on/off this plugin through config.php. 

I've already founded a place where the pane is drawn. And no problems with setting a checkbox there. But the problem is with further interaction: How to store a result of checkbox? How to retrieve inside plugin this result? And all questions of this kind - how to make it working.

If someone knows, plz, let me know!

Thanks!