I don't think trauma is direct factor of empathy. It can influence it, but it does not itself determine whether or not you become more empathetic, it is just instrument in how you react to empathy and how you use it, if at all.
For example; There may be individuals that can look at others and reach out to them because hey! They went through the same thing, they can understand. There are enough evils in this world, I must not add to them. On the flip side, there are others who withdraw from and distrust, or antagonize the world, be it out of fear, retribution, entitlement, pain, whatever it is, letting the trauma shape and harden them.
It doesn't even matter how 'big' or 'small' it is, and 1) some people are inherently like either even without trauma 2) people react differently after all.
Desensitisation is maybe different from trauma, although vacarious and secondary trauma are that I'm thinking about. I dont know whether its possible to cause that through looking at images but I would imagine it is, like if is a live feed its probably like being a first responder and they DO suffer from vacarious trauma and secondary trauma.
Desensitisation is a form of trauma and a reaction to traumatic event, and can be one of the markers of trauma. It's possible to respond to secondary trauma through being say, a witness in a horrible event, but trauma from images is probably stretching it too far, it's like saying you can get traumatized from say, seeing a slasher movie. It seems that there must be some kind of more personal involvement. Being under the
constant threat of possible danger, however, may cause trauma. For example, a war-torn land where news and pictures of houses getting bombed happen every other week.