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It depends on how you are setting up your form.
First, you need to upload the photos that they can download in your own server or an online storage site like Dropbox or Google Drive.
After that, get the direct or download link and paste it in your "Thank You" page. Here's a guide that you can refer to: https://www.jotform.com/help/211-Setting-Up-the-Thank-You-Page
Here's a sample form that you can check: https://form.jotform.com/60966148225965
Here's how my "Thank You" page is setup:
I anchored a text with the downloadable link to a test image. When you click you would be able to download the test image.
If you want to conditionally change the "Thank You" depending on the user's input, and you have specific sets of images to only show on specific rules. Then you can use conditional logic to do that, here's a guide to learn more about conditions: https://www.jotform.com/help/57-Smart-Forms-Using-Conditional-Logic
In the conditions wizard, you'll see the option "Change Thank You Page". From there, you can change the settings based on your users' input.
Let us know if you need more help on this.