Jeff,
I met with my friends, Jim and Pat Swan and in our conversation, I posed the question for you about whether or not any photo's of the 90th existed and thier response was, NO. :( Sorry bout that. There are some pics of individuals on the Illinois In the Civil War website. Also the state of Illinois has a photo of Col. Timothy Omerah as a young man but you have to travel to Springfield to view it.
Wish I had better news. Frank