However, I've got to be that guy because "natural experiments" like this one are tempting and highly suboptimal. Finding a correlation between uploading a picture and higher response rates isn't useless, but it isn't fabulously useful, either: the photos might well be a symptom of an account that someone has put more effort into, and people could be responding to the higher quality pitches, etc.
Happily, there is a solution: the humble A/B test. Take the SAME company with the SAME text targeting the SAME list and let half of them see your mug shot, while half of them get nothing there. THEN you can have a statistically quantifiable amount of confidence that the lift in response rates is actually due to the photo, as opposed to due to unmeasured causes.