[Inkscape-user] How do I color lettering with an image?

I don't know if I worded the subject line accurately so let me describe what I am trying to do...

I want to create lettering (for example, "God bless the USA") which has black stroke paint and white fill. Then, I would like to take an American flag, put it in the background and ONLY have the flag's colors show through the lettering (so it looks like the letters are the colors of the flag).

Does that make any sense?

So, how do I do it?

Thanks for any and all help!