In every book the solution of twin paradox is that one have to accelerate thus two observer does not trace parallel lorentz vectors thus can't be compared. Through GR we get the one who accelerate will sufer time dilation. But what if the other guy is not accelerating but just moving away with rel. velocity and they use EM waves to send the photos of each other isn't still there is Paradox? Think about that.

$$t' = \gamma\left(t - \frac{vx}{c^2}\right)$$
Note that the clock position $x$ appears on the right hand side, so clocks at different $x$ will transform differently.