Subject is a very broad topic.
The subject can be anything: animals, geology, flora, reflection, sports, etc.
Bees and Butterflies on flowers is a big favorite of all photographers.
Use this slideshow by: Clicking on an image, then click the forward arrow (right side) to slide through each photo and the backward arrow (left side) to go back.
Color
Basic color is warm (red, yellow, orange) of cool (blue, green, violet). For me cool is more interesting, but most photographers prefer warm.
Warm images
Cool images
A Mix of warm and cool images
Bridges
Some of these photographs also exhibit aspects of the third topic - composition: leading lines, reflections
Castles
Lone Trees
As to composition, these images exhibit simplicity, balance and leading lines.
Painterly
Sometimes a photo is out of focus, but likable. It can by resurrected by converting it to a painting. I use the software called Topaz Studio, which is now part of Topaz Photo. Other times an image is more enticing when appealing like a painting.
To enlarge an image, click on it and then use the arrows at the side to go forward or backwards.
Iconic
Some subjects are so often photographed, they can be considered iconic. Photographers try to capture them in an unusual way.
Go through these like for the Painterly images.
Windows, Doors and Walls
Weather as a subject
The subjects, flowers, waterfalls and birds have been posted earlier. They can be viewed at the top, click on the name to open the group.
Frescoes
Although not often photographed by others, these are near the top of my favorites.
Churches
Dead Tree and Stump
Glaciers
People
Lighthouses
Natural Bridges and Arches
