@askari
I’m not aware of any Publii plugin that can add images from Unsplash. Depending on how it was / is done, I’m not sure if there might be licensing issues with that method.
Though for me personally, it seems best to download the images you want from Unsplash and then process them as needed before inserting into Publii. Why: some Unsplash images may be massive in file size — far larger than is needed for the web, so using these could hurt your SEO, slow your website down, and so on. While Publii seems to do a superb job at compressing images, I feel its best to get images ‘web-ready’ before inserting into Publii if possible.