One advantage of using the following approach instead of a table is that the images can overlap.
Click one image, and then hold down the Shift key while you click the other. Then, on the Picture Tools > Format tab, in the Arrange group, click Align > Align Middle.
I believe that the Shift-click approach to multi-selection works only if the Position setting of both images is something other than In Line with Text. At any rate, you may sometimes find that you just can't select both images as described above. In that case, check the Position settings. Alternatively, insert a drawing canvas on the page (on the Insert tab, in the Illustrations group, click Shapes > New Drawing Canvas) and then insert your images onto the canvas. You should then be able to select both images and click Align > Align Middle.
(Here, inserting a drawing canvas amounts to the more or less the same thing as changing the Position settings, because the objects on a drawing canvas aren't positioned in line with text.)