Allow apps to use your photos
Some apps and websites can use your photos library to provide you with services and features. For example, an app might use your photo library to help you set up features for a photo editing project. See Control access to your photos.
To authorise an app or a website to use information from your photo library, click OK in the dialogue. If you don’t want to authorise the use of your photo library, click Don’t Allow.
If you allow third-party apps or websites to use your photo library information, any information they collect is governed by their terms and privacy policies. It’s recommended that you learn about the privacy practices of those parties.
You can review and change which apps and websites can use your photo library in Privacy & Security settings.
Choose Apple menu 
in the sidebar, then click Photos on the right. (You may need to scroll down.)