If you could get the link to the picture to be stored in a field in Salesforce (or at least the unique part of that link that points directly to the picture), then you could render that through a token. But you would somehow/somewhere need to have that stored in a field for it to be usable in a token.
Also, the field would need to be on the lead/Contact, not the user. Marketo doesn't have salesforce user object tokens.
I've seen this done by storing all the pictures of your sales reps on a server somewhere, with very strict naming conventions like www.domain.com/imagedirectory/firstlast.jpg, then using tokens like www.domain.com/imagedirectory/{[lead.First name}}{{lead.Last Name}}.jpg to create the image link, which renders the image.
.png)