Try it this way:
Select the first image, adjust the dimension(s) using the Size/Height, Width scroll boxes at the right end of the Picture Tools tab on the ribbon.

Select the 2nd image and press F4.


Works for me.

Actually, only the last adjustment -- height or width -- repeats; that's what F4 does.

But if you change both dimensions in the one pass (i.e. before pressing OK), F4 will repeat the change to both.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]