People think that images for blogs are free but actually there not, well some are not at least. When you google a picture for your blog it is not always free, but her are some sites for pictures.
1.https://pixabay.com/editors_choice/
You can also make your own image from google drawing https://docs.google.com/drawings/d/17k6rzW8gTgA3nW_WUflzc28xc2vVSDkzZySWorWuHvo/edit This is a link for google drawing.