How to check if HttpPostedFileBase is an image

You can check the MIME type (content type) of the uploaded file to ensure it is an image. Images typically have content types like image/jpeg, image/png, image/gif, etc.

For example:

private bool IsImage(HttpPostedFileBase file)
{
    if (file != null && file.ContentLength > 0)
    {
        if (file.ContentType.Contains("image"))
            return true;
        string[] imageExtensions = new string[] { ".jpg", ".png", ".gif", ".jpeg" };
        return imageExtensions.Any(item => file.FileName.EndsWith(item, StringComparison.OrdinalIgnoreCase));
    }
    return false;
}

In your controller action, you can use this method to check if the uploaded file is an image before processing it:

public ActionResult UploadImage(HttpPostedFileBase file)
{
    if (file != null && file.ContentLength > 0)
    {
        if (IsImage(file))
        {
            // Process the image (e.g., save it, resize it, etc.)
            return Content("The file is a valid image.");
        }
        else
        {
            // Return an error message
            return Content("Please upload a valid image file.");
        }
    }
    return Content("No file uploaded.");
}

The above code is a simple way of checking whether a file is an image using file extension and MIME type. However, MIME types can sometimes be misleading, and file extensions can be changed.