With Krita and it's AI Image Generation plugin, it provides a really nice interface for img2img where you can select the area in about 4 different ways, or the whole image, easily change the strength, prompt and negative prompt, select a predefined style or create your own. It's very flexible and intuitive.
Both. And it runs locally on your own machine, so it's entirely private and offline. You also have the option to connect to other people's computers if your hardware is bad.