It can be tricky to tell without measurement. There aren't any guarantees, but here are my guidelines.
Safety-rated X- and Y-capacitors will always have X# and Y# on the markings somewhere. As a general rule, the safety-rated capacitors tend to have many safety ratings on them: your top example has the UL recognized mark, VDE (Germany), DEMKO (Denmark), the Swiss S+ mark, FIMKO (Finland), NEMKO (Norway), etc.
X- and Y-capacitors usually don't explicitly have a voltage rating on the package, since the X- and Y- rating implies their use (mains circuits up to 250VAC nominal, for instance). These should be the easiest to identify of the three types you've mentioned.
Ordinary ceramic capacitors won't have a safety rating, and usually have some marking indicating their voltage rating. If the part is a capacitor (regardless of type), the part number will tend to be a multiple of picofarads as Zebonaut has explained.
A MOV part number usually doesn't 'look' like it corresponds to a capacitance value. They will have some safety marks on them as well. It will often have a 'smooth' case like a Y-capacitor.
An NTC can best be checked by measuring for resistance - a good Y-cap and a good MOV will appear open-circuit to a multimeter. Many MOVs won't have safety marks and part numbers that don't look like capacitor values. Most MOVs that I've seen have 'rough' cases - sometimes the only way I can quickly tell a MOV from an NTC is by the roughness of the case.
No matter what, once you've made your identification it's always best to try and look up the part number - putting the wrong part in an application can lead to spectacular failure.