Besides the fact that they look different, in what way are they different? I would prefer answers about components, how they are powered, and function.
While they look quite similar (as they're both bipedal walkers), each is designed for a somewhat different - and distinct - purpose. The All Terrain Scout Transport (AT-ST) is primarily a reconnaissance and patrol vehicle; whereas the All Terrain Defense Pod (AT-DP) is mainly used to defend a location or site (as well as for training Imperial cadets).
Although armaments can be modified, typically the AT-ST is equipped with a chin-mounted medium blaster (with a range of up to two kilometers), as well as side cannons (to take out enemy vehicles and ground troops at close range). And the AT-DP is usually armed with a single heavy laser cannon (known as a Maad-38).
Both vehicles have a crew of two (with a maximum combined weight of 200kg). The AT-ST stands 8.6m in height, whereas the AT-DP is 11.6m tall. The AT-ST has a mass of 12,100kg; and the AT-DP has a slightly smaller mass, at 11,200kg. Both are capable of speeds up to 90km/h.
The AT-ST also has a cargo capacity of 500 metric tons while the AT-DP doesn't have any cargo capacity. There was also another model of AT-ST called the AT-ST Mark III that was equipped with experimental armor that provided more speed and durability as well as twin heavy laser cannons. It was piloted by veteran crews and excelled against most targets.
The All Terrain Scout Transport is loaded with much more powerful weapons and a number of them as well. It has a chin mounted blaster cannon, rockets on the left side, and a rotary grenade launcher with up to 8 grenades. While the All Terrain Defense Pod has one singular heavy blaster cannon. It is naturally taller than the AT ST, but it’s mass is a lot smaller because the AT ST has a bigger load of weaponry. The AT ST is used as patrol, scouting, and frontline attacks. The AT DP is used as a defense walker to defend Imperial outposts as well as training new Imperial cadets or pilots.
The AT-DP had a very flawed design, due to its enormous height, it was very easy to tip over. it was also very lightly armed, with only one single heavy blaster cannon.