Hello Jimm,
Thank you for your question about background images on your blog page. The background image you’re seeing is likely the background image for your theme, which means it will be the same across your whole site and any page you create. This is meant to keep a consistent look across pages. If you would like your blog to have a different look and feel you can use the Multiple Themes plugin or consider installing a dedicated WordPress blog in a subdirectory like “/blog”.
Best,
Christopher M.