Hey Keith,
Of course this is possible, just follow those steps :
1 - Add a gallery component on your page
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2 - Double click on your gallery > Edit gallery design > Check that on item click is set to "open link" and then scroll to caption to edit how your legend appears
f8fb9e12-57a3-43d2-b46b-41b19550ae53-image.png
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3 - Previous OR Double click again on your gallery > Edit gallery content > Add your images and on the left you can fill the content input, this is your legend
45b4d414-cd96-4113-a22d-504bb4880b2c-image.png
4 - To add a link to a popup, click on link and select open in "modal" (a modal is a popup), you can link it to any page you created or external pages as well
Don't hesitate if you have further questions!