You need more teaching and more practice on the wards, then. Subtle signs can be really hard and for definitive diagnoses of things like cancer do require samples yes, but lobar consolidation, oedema, effusion, solid tumour masses, pneumothorax, all do look different yes and you should be able to tell the difference by the end of med school.
There are some reasonable websites (though be cautious of getting bogged down in technicalities) and if you always ask about each XR you see on the wards you should make progress in good time.