Validation attribute for imagefile

using System.Collections.Generic;
using EPiServer.Core;
using EPiServer.Validation;
using EPiServer;
using AlloyDemoMVC.Models.Media;

namespace AlloyDemoMVC.Business
{
    public class ImagePropertyValidator : IValidate<ContentData>
    {
        /// <summary>
        /// Validation attribute that checks Imagefile properties for null.
        /// </summary>
        /// <param name="page"></param>
        /// <returns></returns>
        IEnumerable<ValidationError> IValidate<ContentData>.Validate(ContentData page)
        {
            string errorMessageTemplate = @"The file ""{0}"" is missing Copyright info!";
            ValidationErrorSeverity severity = ValidationErrorSeverity.Warning;
            List<ValidationError> errors = new List<ValidationError>();
            PropertyDataCollection pageProperties = page.Property;

            foreach (PropertyData propertyData in pageProperties)
            {
                //Built-in properties that we want to ignore
                if (propertyData.OwnerTab == -1) continue;

                //ContentArea
                if (propertyData.PropertyValueType == typeof(ContentArea))
                {
                    var contentArea = (ContentArea)propertyData.Value;

                    if (contentArea.Items != null)
                    {
                        foreach (var item in contentArea.Items)
                        {
                            var content = item.GetContent();

                            if (content as ImageFile != null)
                            {
                                if (string.IsNullOrEmpty(((ImageFile)content).Copyright))
                                {
                                    errors.Add(
                                        new ValidationError
                                        {
                                            ErrorMessage = string.Format(errorMessageTemplate, ((ImageFile)content).Name),
                                            PropertyName = propertyData.Name,
                                            Severity = severity
                                        });
                                }
                            }
                        }
                    }
                }
                //ContentReference
                else if (propertyData.PropertyValueType == typeof(ContentReference))                
                {
                    var reference = propertyData.Value as ContentReference;// page.GetValue(propertyData.Name) as ContentReference;

                    if (!ContentReference.IsNullOrEmpty(reference))
                    {
                        ImageFile file = null;
                        var locator = ServiceLocator.Current.GetInstance<IContentRepository>();

                        try
                        {
                            file = locator.Get<ImageFile>(reference);
                        }
                        catch (Exception)
                        {
                            file = null;
                        }

                        if (file != null)
                        {
                            if (string.IsNullOrEmpty(((ImageFile)file).Copyright))
                            {
                                errors.Add(
                                        new ValidationError
                                        {
                                            ErrorMessage = string.Format(errorMessageTemplate, file.Name),
                                            PropertyName = propertyData.Name,
                                            Severity = severity
                                        });
                            }
                        }
                    }
                }
            }

            return errors;
        }
    }
}