ksnip
ksnip the cross-platform screenshot and annotation tool
...Add watermarks to captured images. Global hotkeys for capturing screenshots (currently only for Windows and X11). Tabs for screenshots and images. Open existing images via dialog, drag-and-drop or paste from the clipboard. Run as a single instance application (secondary instances send cli parameter to primary instance). Pin screenshots in frameless windows that stay atop other windows. User-defined actions for taking screenshots and post-processing. OCR support through plugins (Windows and Linux/Unix). Many configuration options.