If it's the same person, the photos were taken around 20 years apart.

The 1st photo is an officer in a Heer (German Army) cavalry unit sometime in the later 1930s or early 1940s - his peaked officer's cap has the red-black-white rosette of the German armed forces, the Nazi eagle and swastika, and the totenkopf (literally "death's head"). The totenkopf had a history that long predated its adoption by the Nazis - it was very popular with Prussian cavalry units as far back as the mid 18th century. Post-WWI, it was kept as a symbol by several cavalry units in the Reichswehr. When the German armed forces began to mechanize, the death's head insignia was also adopted by the panzertuppen, the tankers.

It was also popular with right-wing Freikorps militiamen during the tumultuous post-war period. This may have influenced its adoption by the Nazis' Schutzstaffel (SS). The cap of Waffen-SS cavalry officers looks very similar to the one in the photo.

The second photo is from the last half of WWI (the simpler uniform with the M15 Tunic is a solid clue) - the young man is a German cavalry officer. He's got cavalry boots and the death's head on his cap, this cap is similar to the one in the photo - although the one he's wearing would be in gray, not black.

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Hello there! As your question is related to looking for identification/information regarding military personnel, our Guide on Military Identification may be of use to you. It provides a number of different resources, including how to request service records from a number of national agencies around the world, as well as graphical aids to assist in deciphering rank, unit, and other forms of badges or insignia. While the users here may still be able to lend you more assistance, hopefully this will provide a good place to start!