ExpressJS / NodeJS Redirect Image

Is it okay for an img to have src value with redirect to another page?

In view, I have img:

<img src='/images/fileName'/>

In app.js

app.get('/images/:fileName', subject.image);

This is my route:

exports.image = function(req, res){
    var fileName = req.fileName;
    fs.exists(fileName, function(exists){
        if (exists) {
            res.sendfile(imagePath);
        }else{
            res.redirect('http://gravatar.com/avatar/_some_hash');
        }
    });
}

My code works, but is it okay to use res.redirect if image does not exist?

Thanks