Converting between image file types in c#
private void profileImgUpload(HttpPostedFile profileImg)

String[] allowedExtensions = { ".png", ".jpeg", ".jpg", ".gif" };
for (int i = 0; i < allowedExtensions.Length; i++)
    {
        if (FileExtension == allowedExtensions[i])
            FileOK = true;
    }
}

if (FileOK)
    profileImg.SaveAs(physicalPath + "newAvatarTemp.png");