My horse was diagnosed with mild changes in the navicular bone, the image the vet showed me was front on I don't think you would see the navicular bone from that angle enough to know for sure, and yes ycbm is right it's often soft tissue involved as well so vets will often scan or mri to get a proper look at what's going on.
It's more than that Pinkvboots, it's now known that the condition of the navicular bone is rarely the issue at all They've known for forty years, since I had one with it, that x rays didn't correlate with lameness. Then we got MRI and it became obvious why.