I use Canva , for my Blog featured images, and I also use these pictures for Pinterest, and Twitter to promote my blog.
They have many beautiful options. I go to templates, and I click on Instagram post. Then I click "create blank Instagram post. I choose my font, and I click on pictures, and pick a picture that pertains to my blog post. I use the free option. You can also pay to have unlimited access on Canva, for $119 a year. I use snippet tool on my computer to save the image or I download it. Make sure you download it as a JPG.
by Michelle gast