Yes you can. You need to obtain your admin access token by using the Graph API explorer (https://developers.facebook.com/tools/explorer) and with a call to
https://graph.facebook.com/{adminfacebookid}/accounts
this will list all pages and apps your admin has access to. Look for the fan page in question and copy the accessToken.
Next get the albumid by clicking on the id of the page, then adding /albums to the request
armed with this you can then post the image data to the url, using the facebook web client
like this
protected void PublishToPublicGallery(string accessToken, string filename, long albumId, string imagename)
{
var facebookClient = new FacebookClient(accessToken);
var mediaObject = new FacebookMediaObject
{
FileName = filename,
ContentType = "image/jpeg"
};
var fileBytes = System.IO.File.ReadAllBytes(filename);
mediaObject.SetValue(fileBytes);
IDictionary<string, object> upload = new Dictionary<string, object>();
upload.Add("name", imagename);
upload.Add("source", mediaObject);
var result = facebookClient.Post("/" + albumId + "/photos", upload) as JsonObject;
}