Left and right hand: why read both
Palmists read both hands and compare them. Cheiro put it this way: in a right-handed person, the left hand shows what they were born with, and the right shows what they have made of it.
In a left-handed person it is the other way round. That is why Benham spoke not of left and right but of the dominant hand, the one used for writing and work, and the other one.
Read your own palms from a photo. The short reading is free, no account needed.
What usually differs
Most often, the heart line. On one hand it is curved and lively, on the other straight and calm. Someone may be passionate by nature, for example, yet have learned to hold back.
The head line can differ too: sloping downwards on one hand and running straight on the other. Then there is more imagination in the person than they allow themselves.
The life line is compared by depth. Where it is deeper, there is more strength.
Why one hand is not enough
The dominant hand shows who a person is now, but not what they gave up. The other hand shows who they might have become, but not who they are today. The picture only comes together from the two.
Photograph both hands in the same light. Otherwise the difference between the photos will be a difference in lighting, not in the hands.
Related reading
Read your own palms from a photo. The short reading is free, no account needed.