如何获得自定义验证器来验证客户端

在我的Mvc项目中，我有这样的模型：

namespace CameraWebApp.Models
    public class Images
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int ImageId { get; set; }
        [Required(ErrorMessage="Please enter your first name")]
        public string SubmitterFirstName { get; set; }
        [Required(ErrorMessage = "Please enter your surname name")]
        public string SubmitterLastName { get; set; }
        [ExistingFileName]
        public string NameOfImage { get; set; }
        [StringLength(140, ErrorMessage="Please reduce the length of your description to below 140 characters")]
        [DataType(DataType.MultilineText)]
        public string DescriptionOfImage { get; set; }
        public string ImagePath { get; set; }
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public DateTime DateAdded { get; set; }
    }

正如您所看到的，NameOfImage属性具有属性[ExistingFileName]，这是一个自定义验证器，该验证器的代码如下：

//Overiding isValid to make a custom Validator
protected override System.ComponentModel.DataAnnotations.ValidationResult IsValid(object value, System.ComponentModel.DataAnnotations.ValidationContext validationContext)
{
    if (value!=null)
    {
        string fileName = value.ToString();
        if (FileExists(fileName))
        {
            //If the file exists use default error message or the one passed in if there is one
            return new ValidationResult(ExistingImageErrorMessage ?? defaultExistingImage);
        }
        else
        {
            return ValidationResult.Success;
        }  
    }
    else
    {
        //If theres no value passed in then use error message or default if none is passed
        return new ValidationResult(ErrorMessage ?? DefaultErrorMessage);
    }
}
bool FileExists(string fileName)
{
    bool exists = false;
    //A list is passed all the images
    List<Images> images = cameraRepo.getAllImages().ToList();
    //Loops through every image checking if the name already exists
    foreach (var image in images)
    {
        if (image.NameOfImage==fileName)
        {
            exists = true;
            break;
        }
    }
    return exists;
}

在以下代码中，客户端正在验证以前的每个属性：

@using (Html.BeginForm())
{
<div id="errorMessages">
@Html.ValidationSummary(false)
</div>
<label>base64 image:</label>
<input id="imageToForm" type="text" name="imgEncoded"/>  
<label>First Name</label>
@Html.EditorFor(model => model.SubmitterFirstName)
<label>Last Name</label>
@Html.EditorFor(model => model.SubmitterLastName)
<label>Name of Image</label>
@Html.EditorFor(model => model.NameOfImage)
<label>Image Description</label>
@Html.EditorFor(model => model.DescriptionOfImage)
<input type=button id="button"value=" Camera button"/>
<input type="submit" value="Click this when your happy with your photo"/>
}
</div>
@Html.ActionLink("gfd!!", "DisplayLatest")
<script src="@Url.Content("~/Scripts/LiveVideoCapture.js")" type="text/javascript"></script>

除了我的自定义验证[ExisitingFileName]之外，所有验证都在客户端工作，我不知道为什么？有人知道为什么会这样吗？提前感谢！