Hi MehulG. First of all, I’d like to highlight that it’s not our plugin’s fault that your images look so pixelated; you’ll need to use higher-res images in order to prevent this.
Now, in case you’re wondering: why is this happening? Well, all themes (and the Iconic Theme is no exception) define one or more featured image sizes: the featured image will have a certain size in the latest posts page, another size in the single view, another size in this widget, and so on. When a featured image is uploaded to the Media Library, WordPress may scale it down and generate several thumbnails (one for the latest posts page, another for the widget… you get the idea, right?), but it never scales it up.
What if the image is smaller than one of those sizes? Well, WordPress will use the biggest image available, but it will probably won’t scale it (actually, that depends on the theme, but they usually don’t scale them up).
Our plugin uses your theme’s information and always scales the featured image to W x H (without modifying the image’s aspect ratio). We always scale it because there’s no way we can now if the image is bigger or smaller than the container where it’ll be displayed. If the image is bigger than W x H, the image is reduced and it simply looks great. If, on the other hand, it is smaller, then it’s scaled up and thus pixelated.