Ok, titobay, lets look at this.
Is she your husband's daughter from another relationship? I would assume so, since you are her step-mother, thereby making him her biological father. If he loves her and is proud of her, his carrying her picture would seem completely within the scope of normal. The question is--Why should this be a concern to you personally?
My husband no longer carries a wallet, though when he did there was never a picture of me in it. He had pictures of our two kids at various ages. And I only remember that because often times he would have me retrieve something from his wallet that he wanted to show me, or have me clean it out because it was a mess and falling apart. Otherwise I considered his wallet HIS PERSONAL PROPERTY.
Regardless of whether or not he has (had) my picture in his wallet does not make me wonder if he thinks of me "while I'm away from home". I don't quite know what that is supposed to mean. My picture does not need to be with my husband at all times to remind him that I exist in his life or that I am his wife. Though we fight frequently, I know daily he thinks of me, whether he is calling me, texting me, or sending me an email from his job. There are some days I hear nothing, but my concern then is not whether he is thinking of me, but whether he is okay, wherever he is or what he is doing.
If this is a question based on your own personal marital issues, you really need to open a line of communication with your husband to let him know that you are troubled by this simple issue. He will likely be ticked off to find out you have been going through his wallet, which you really should not do. He may even be totally surprised, and perhaps a little put off that you feel that way about his daughter's importance in his life.
Sorry. I did not mean to preach. I am not a marriage counselor, but I have spoken to many friends and counselors through the years and all have had input on various issues in marriage. You need to go carefully here.