> A photo may also be referred to as a ‘photograph’, this is a combination of the Greek words for light and drawing; A photograph is a drawing made of light.

Source https://shuttermuse.com/glossary/photo/

According to Wikipedia the two words mean the same thing:

https://en.m.wikipedia.org/wiki/Photograph

Photo seems to be the more popular version lately which is hardly surprising:

https://books.google.com/ngrams/graph?content=photo%2Cphotog...