Personally, nearly all my profile pictures are just fictional character i like + bi flag and/or hammer and sickle in the background so idk much in the way of “professional” pfp’s lol but in that scenario I’d probably go with some sort of historical photo of a leftist figure, preferably someone less recognizable to your average lib depending on how “professional” the environment is. As much as i love ol’ joe he was absolutely correct in saying a pile of rubbish would be heaped apon his grave. So pick someone deemed more “sensible”.

Can’t help you with your specific request for leftist inspo since my profile pic is a photo of my dogs lol but I can answer the “why do you use it” part:

Because they’re good dogs and they look hilarious in this specific photo. They’re so focused because I was holding a ball and were waiting for me to throw it lol

“Solemn Oath”, Red Army recruitment poster from 1918. Translation here.