Some images on Pintrest are under free licenses, many are not. Making and distributing copies of images that are not under free licenses would be at least a technical infringement of copyright. (In general, making a copy of a protected work is infringement, unless you have permission, usually some sort of license.) As you are not transforming the images, and are not commenting on them, and are doing this as part of a commercial enterprise, this probably would not count as fair use under US law (you don't state where you are located). Given that the original images are not being sold, and so you are not harming the market for them nor causing any economic damage, the likelihood that you would be sued may not be large, and the damages might be small even if you were, but neither of those would be a sure thing.
There are many images on the net that are distributed under a free license. You would be much safer to search out and distribute such freely available images. Or you could distribute links to the original images, as @ohwilleke suggests in a comment. In either case you should be safe from suit.
The person who could potentially take action against you would be the photographer who created the images, or the copyright holder if the copyright has been transferred, or the image was a work made for hire.