Facebook image compliance checker
With this tool, you can check the "20% of text" compliance of your cover image, promoted page or page post and sponsored stories. As stated in Facebook Advertising Guidelines: "Ads and sponsored stories in News Feed may not include images comprised of more than 20% text."
Our tip: Though the guideline says that the restriction relates only to News Feed, we suggest you to check your ads images appearing in the sidebar. These ads may appear as sponsored in the News Feed and that might be a problem.
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Statement: This application is in no way sponsored, endorsed or administered by, or associated with, Facebook.