After iOS 10 version you can also display images, GIF or videos in your notification. you need to do following things in your project.

Step 1 : Add NotificationServiceExtension in your project targets.

step 2 : Write following code in your NotificationServiceExtension.swift file.

import UserNotifications
import MobileCoreServices
class NotificationService: UNNotificationServiceExtension {

var contentHandler: ((UNNotificationContent) -> Void)?
var bestAttemptContent: UNMutableNotificationContent?

override func didReceive(_ request: UNNotificationRequest, withContentHandler contentHandler: @escaping (UNNotificationContent) -> Void) {
self.contentHandler = contentHandler
bestAttemptContent = (request.content.mutableCopy() as? UNMutableNotificationContent)

if let bestAttemptContent = bestAttemptContent {
// Modify the notification content here...
//            bestAttemptContent.title = "\(bestAttemptContent.title) [modified]"
//
//            contentHandler(bestAttemptContent)

// Get the custom data from the notification payload
if let notificationData = bestAttemptContent.userInfo["data"] as? [String: String] {

// Grab the attachment
if let urlString = notificationData["attachment-url"], let fileUrl = URL(string: urlString) {

// Download the attachment
URLSession.shared.downloadTask(with: fileUrl) { (location, response, error) in

if let location = location {
// Move temporary file to remove .tmp extension
let tmpDirectory = NSTemporaryDirectory()
let tmpFile = "file:".appending(tmpDirectory).appending(fileUrl.lastPathComponent)
let tmpUrl = URL(string: tmpFile)!
try! FileManager.default.moveItem(at: location, to: tmpUrl)

// Add the attachment to the notification content
if let attachment = try? UNNotificationAttachment(identifier: "", url: tmpUrl) {
self.bestAttemptContent?.attachments = [attachment]
}
}
// Serve the notification content
self.contentHandler!(self.bestAttemptContent!)
}.resume()
}
}

}
}

override func serviceExtensionTimeWillExpire() {
// Called just before the extension will be terminated by the system.
// Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
if let contentHandler = contentHandler, let bestAttemptContent =  bestAttemptContent {
contentHandler(bestAttemptContent)
}
}

}