[bryced]

This is itself it's own finetuned version of SD so now it won't work with alternative versions. img2img works by just running normal stable diffusion img2img on a noised starting image. As such it destroys information at all parts of the image equally. This new model uses attention mechanisms to decide which parts of the image are important to modify. It can leave parts of the image untouched while making drastic changes to other parts.

[caxco93]

Well, to be fair you can use feathered bitmap masks for img2img with some UIs (automatic1111)

[pfd1986]

Perfect explanation, thank you!