Here is how to do it:
1. Find out your type if you have not done it yet.
2. From the main menu, select the third button - "Check if the color(s) match". Please note that this option will become available only after determining your color type.
You can copy and paste a photo from another app if it allows copying.
Alternatively: some iOS/iPadOS apps allow you to share the content with Choos! For example, you can open a photo in your Photos library and send it to Choos! using the share button. You may need to enable this destination first ("more" button in the iOS/iPadOS share menu).
This sharing function may be disabled for some websites and online stores. Also, some versions of iOS/iPadOS provide variable support. Do not worry - the app has a built-in workaround - it will open the website on a new screen and then take a screenshot. Adjust the view appropriately (pan, zoom, close any pop-ups, etc.)
Or take a screenshot manually, and you can send it directly to Choos!