|Just a Rifle|
According to the Encyclopedia Brittanica, an "assault rifle" is a "military firearm that is chambered for ammunition of reduced size or propellant charge and that has the capacity to switch between semiautomatic and fully automatic fire." By design, they are easy to carry, have a high rate of fire, carry a large amount of ammunition in the magazine, and reload quickly by changing the mazagine. The only distinction that the civilian model at the bottom has from a military weapon is that the civilian weapon is not capable of fully automatic fire.
The first (top) rifle in the image is a lever-action rifle. Today, they are designed mostly for hunting at moderate range. Looking at online advertisements, they are available in a wide range of calibers. The magazine typically seems to hold about 10 rounds of ammunition, which would have to be loaded into the weapon individually. The weapon must be cocked by lowering and raising the lever before every shot, which will limit its rate of fire, but if you went on a crazy shooting spree with this weapon, you could probably shoot ten people before you had to stop and reload, allowing potential victims to either escape or attack you.
The second is a bolt-action rifle, also typically used for hunting these days, although military sniper rifles are also frequently bolt-action rifles. Generally used with a scope, they are accurate at long ranges. The World War 2 era rifle that I own myself holds 5 rounds in the magazine; these can be loaded individually or loaded all at once using a "stripper clip" that holds all five rounds together in the right orientation for loading. These rifles typically use a powerful cartridge like the .30-06 round (7.62 mm). The bolt-action must be manually worked before every shot. If this was your weapon on a shooting spree, you could potentially hit from a large distance, but you would still probably only be able to hit a few people before your victims scrambled for cover.
And finally, the third weapon, which is also "just a rifle". The design is military, although the fully automatic fire capability is removed for the civilian market. For the military, it is intended to fire a lot of bullets in a short time at moderate range. As far as I know, civilians typically buy such weapons for home defense, plus just liking the idea of owning such a weapon. The AR-15 fires .223 caliber ammunition (5.56 mm): a small but fast bullet. The civilian model is semi-automatic, loading a fresh round into the chamber after every shot, allowing you to fire as quickly as you can aim and pull the trigger. I found online ads for AR-15 magazines holding anywhere from 10 to 40 rounds of ammunition. By design, the magazine can be detached when empty and quickly replaced with a full one. If this was your weapon on a shooting spree, and you had practiced with it, you could reasonably expect to shoot dozens of people.
I am not against gun ownership. As I said, I have a rifle myself. In it's time, my Mosin-Nagant was a military combat rifle.
I am against bad arguments for anything. Pretending that there is no difference between the three rifles in that picture is dishonest. You don't need 40 rounds of .223 semi-automatic fire for deer hunting; a weapon like the AR-15 is meant to kill people.
Sure, "assault" is an action, but it is also a design specification.