All pages and content for Cognito Forms are always served over HTTPS. For example, clicking this link:
will automatically redirect you to:
However, if you add images to your forms by specifying a URL to your images from your website, instead of uploading your images, these links must also be HTTPS. If they are not, you will receive a security warning.
If this is not the problem in your case, please submit a support request so we can take a look at your specific form, and please provide a link to where your form is embedded in your secure website.
http://help.cognitoforms.com/request-helphttps://www.cognitoforms.com/support
