Adding an image to a blog post or to a website page is a “good thing”. Ideally relevant to the content, a photo or picture can draw the reader in by breaking up the text and making the whole page more readable.
One thing you must not do, however, is use other people’s images without their permission. Google Images is not the place to find your images. Instead go to Photo Pin and find something suitable there, download the best size for your needs (larger if your home page shows a larger image, perhaps in a slider), copy and paste the credit into your page/post, and away you go.
The following video takes you through how to add an image from Photopin to a blog post: