We are but a bunch of willing volunteers who over years of researching, restoring old photos and helping with online dating, we have acquired a measure of knowledge based on information gathered either from our own or others dated photos, or online resources. As a Collector of old postcards, Carte de Visites and Cabinet cards I have, in common with others. Gained some knowledge, albeit it limited, on dating photos within a couple of years.
As dating photos is not an exact science, there will always be anomalies and room for error. Older people didn't keep up with fashion so dating by clothing can be hit and miss. Children often wore altered or handed down clothing will also create difficulties when trying to date a photo with any accuracy. Card stock too can be misleading as they are often still in use long after their sell by date.
Many people misguidedly believe that if a photo is in a family album, then it must be a family member, this misconception is easy to understand, but people swapped and collected photos to add to their collection. I have a rhyme in a book that supports this theory which I will post at a later date.
All we can offer is a best guess on date of photo and age of sitters give or take a couple of years based on what we know of the fashion of the day which can, in most cases lead to posters being able to identify possible candidates.
Carol