@jennymwine It is certainly a very beautiful image that shows a high level of skill. As for professional, as @evilrobot said that is highly subjective.
First of all, professional what? Depending where you're sending this postcard it might be the completely right or wrong style. It does look a bit older than say for children's book illustration. I could see this image in an illustrated novel, something a bit older but with pictures. They often have these black and white illustrations in them. And again as @evilrobot said much of it is going to depend on your entire portfolio as a whole. You want to make sure your postcard image shows a style that you want to draw in the most, and that is representative of what they'll find in your portfolio. You want your portfolio to show a variety of subjects, but in one strong signature style that is consistent throughout the whole portfolio. This image intrigues me but I'd need to see more because if I'm an art director I'll ask myself "Ok but can they do color? Can they do characters?" etc. Also while you're obviously very skilled at landscapes, be careful that your portfolio does show a lot of characters. I made this mistake the first time I sent my portfolio: I'm very well-versed in perpective and decided to show that off with grand illustrations showing detailed and impressive backgrounds. Result: I was told by multiple people that I didn't have enough emphasis on characters in my portfolio, and that while backgrounds are important, in a children's book connecting with the characters is everything so art directors NEED to see your characters in your portfolio more than they need to see your backgrounds. Again it depends what and where you're even applying for, you didn't specify what genre and target audience you're aiming at...
