I personally like to see a picture, it is worth a thousand words right? Avatars are OK from a branding perspective but I think most people like to see a picture. Yes, it doesn't mean the picture you are seeing is really the person or one they stole from another site. There are a LOT of marketers who use different names in different niches but do use their own picture. I have come across a few or the other person stole their picture.
The real question is: Does that make you trust them less?
Or does the fact you can see someones picture and get to know them from what they have online that also has their picture. Forums, social media, sites, and whatever else there is make you trust them more?
There are quite a few sites that have mystery owners as nobody really knows the person who runs them or what they look like. Then there are the publicity hounds who plaster their faces wherever they can.
It is an unfortunate part of the human psyche to want to connect a face to what they do. We remember faces faster than a name in most instances; liker we can talk to someone we know we have seen before and don't want to embarrass ourselves by asking their name again because we forgot.
Then you get into the argument of your picture will determine your conversions. If you aren't familiar with it, it goes like this - people may not like your race, color, sex, dress, makeup, hair color, hair style, etc. and will not buy from you because of those things. So just use an avatar and you are set to go right?
Just from this discussion it is obvious some people will not buy from you because you have an avatar.
In my opinion, it doesn't matter what you do - some people WILL NOT BUY FROM YOU! They can use whatever excuse they want, it is their excuse and they are welcome to it. If you try to please everyone, you will end up pleasing no one.
If people are scared away by my bald head, GREAT! They are not my audience. If people are scared away by my boldness, they are not my audience either. If people are scared away by my avatar, they are not my audience either. If people are scared away by my emails, they are not my audience either.
In the end, whether you have a picture or not really doesn't matter because someone will not like it and not buy from you for either option.