If your images are automatically being linked to somewhere when adding images to your pages, the most likely cause for this is with how you are adding the image. When selecting your image in the media library window, please check the settings under "Attachment Display Settings" on the right side.
WordPress may be re-using your setting from another image insertion somewhere else on your site (such as in a blog post or another page for example).
Select "none" for the link option as seen here:
Also make sure you have selected the correct image size as well. Selecting too small of a size will make your image look blurry/grainy especially when using it for a background image.
If you have further questions or need any help please reach out to our support team