That kind of effect, which I think is called a "cast shadow" would indeed have to be created in Photoshop. Save as a PSD file and place in InDesign.
As I Windows user I don' know anything about Pages, but you can make a copy of the image in ID, then reflect it vertically, crop and add a gradient feather, I would think.
You can do it as Peter says, but you'll have more control over the appearance in Photoshop, if you should learn that application.
I'll have a look at Photoshop (something I've not dared to do for years). If it's too much for me, I'll try your suggestion, Peter.
Thank you both...