Check your license from shutterstock what you are allowed to do with these images. They allow you, for appropriate payment, to publish their original images on your website. There is no reason why you couldn't ask them for a license to create an image derived from their original and publish it on your website.
Anyway, according to your description, you created a derived work of the shutterstock images. Which is copyright infringement unless your license from shutterstock allows this. You have of course copyright on your modifications, but shutterstock also has a copyright on your work, because it is derived from theirs. If you have no license to create a derived work, then publishing it makes the situation worse.
To answer your question: Legally, by getting an appropriate license. Illegally, by creating a work with so little similarity that you are not suspected.