strike iny or outy

[Roety]

I keep seeing coins that the reverse side is either raise or sunk on. 
some are the same coin.   is this an optical illusion or are some struck with a sunken die
see the attached (posted photos)   . What's up with this?  how does it effect value .
I know these are silver Roman coins, I post this question here because I know there are experts here.
Ok now the photos don't look like a good example of what I was seeing.  (they are both outys)
Thanks

[Victor]

maybe you are talking about brockages

below are examples of brockages, which happened when a coin stuck to the die which resulted in the next coin struck bearing an incuse design of the stuck coin. This usually happened with the upper die (which struck the obverse) since it was harder to notice a stuck coin on the top die than on the bottom die.