ALONE
The Merriam-Websters dictionary lists several definitions for ALONE. 
The first definition and the one this image grouping focuses on is :
                separated from others - Isolated
There appear to be many variations on the concept of Isolated. One can be isolated from other people and still be not completely Alone. It also depends on the observer's frame of reference. While the observer may say the subject is Alone, the subject may vehemently disagree, and visa versa. I find it interesting that, by implication, one can only not be Alone unless there are others, implying their kind, around.

Some examples are:
In image 1, the religious man is sitting on a wall, alone, immersed in prayer with his God(s).
In image 2, the woman is waiting, alone, communicating with someone.
In image 3, the woman is sitting on a pedistal, alone, staring outwardly and, perhaps inwardly as well.
In image 4, the man is lying in the center of a public square, alone, asleep, being glared at by others on the square. At this point, with the exception of being cast off in the middle of a lifeless desert or planet, he is probably as alone as it's possible to be.
In image 5, a lone man casts his line into the sea, surrounded by no one but the birds and, he hopes, the fish he hopes to catch.
In fact, unless we stick rigidly to the "Surrounded by Others: Others being like the subject", it is frightfully difficult to be truly alone It is almost impossible if we include other species into the concept of companionship. Being cast off on an uninhabited planet or in the middle of a lifeless desert should qualify, as should being deceased and buried 6' down. Of course, in the case of the burial, unless it was a sole burial, the deceased would be surrounded by the other decedents and, therefore, not strictly Alone.
So there is a contextual meaning to Alone. Does being surrounded by decedent's excuse you? Does being surrounded by thoughts excuse you? Does being surrounded by birds or fish? Does being surrounded by people who despise you qualify or excuse you from being alone? 
How do these variations on Alone affect the individual? A individual may be made to feel alone by expulsion from a family or group. By the results of an accident or surgery that significantly alters them from their "normal" self and makes them pitted or looked down on by their societal group.Even by something as simple as a comment to the group making the person an outlier can cast one out into singularity.