Could it be this?

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

Under photo enhancement, McKenzie notices Cole in the background of the picture and identifies the gun Cole is carrying as a .357 Magnum from the 1980s. Despite this, chemical and spectroscopic testing indicates that the photograph is at least 100 years old. McKenzie becomes convinced that Cole is a time traveler.

Could it be Timestalkers (1987)?

Under photo enhancement, McKenzie notices Cole in the background of the picture and identifies the gun Cole is carrying as a .357 Magnum from the 1980s. Despite this, chemical and spectroscopic testing indicates that the photograph is at least 100 years old. McKenzie becomes convinced that Cole is a time traveler.