Snaps are normally fast and fleeting photos. The concept of this application is that each photo disappears after a maximum period of 10 seconds. Anyone can take screenshots and save the photos, but this maneuver notifies the sender that you have saved their photo. If you want to save photos without the sender being notified, know that several ambitious app developers have made this possible.
Remark:
As Snapchat does not want the users to be able to save the photos, the app regularly hacks the methods which are aimed at bypassing the system. As a result, these quickly become obsolete.
Steps
Method 1 of 2: Android

Step 1. Open the Settings menu on your Android device
To install an app designed to stealthily save Snaps, you must allow the installation of apps from unknown sources (i.e. not from the Google Play store). In fact, Snapchat has asked Google to remove these types of apps from the Google Play store.

Step 2. Select the Security option in the Settings application
This opens the menu Security of your device.

Step 3. Check the Unknown sources box
You will be asked to confirm that you want to allow this. Confirm to allow installation of apps from unknown sources.

Step 4. Go to apkmirror.com/apk/casper-io/ in your Android browser
This is the APKMirror site of the Casper.io app. Snapchat has asked the developers at Casper to remove their app from their website, but you can download it from APKMirror, a trusted Android app repository.

Step 5. Download the latest version of Casper
Push the button Download which is next to the most recent app version. Make sure you have the most recent version, as older versions should no longer work.
- Once you have tapped the icon Download, you must press again Download to confirm. Your browser might ask you to accept the download, which you should do.

Step 6. Install the downloaded APK file
Open your notifications screen and tap on the notifications Completed downloads. The installation of Casper will start. It will work like any other application since you have authorized applications from unknown sources.

Step 7. Create a new Google account before launching Casper
In order to use Casper, you must provide your Google account and password. This is essential to be able to access Snapchat services. The developers at Casper themselves recommend creating a new account just for Casper, for security reasons.
It only takes a minute or two to create a new Google Account. See Create a Google Account to learn more

Step 8. Launch Casper and enter your Snapchat login credentials
You will need to enter your Snapchat username and password before Casper can log into your account.

Step 9. Enter the Google account you just created
You must enter the username and password in order to continue. Once it's done, Casper logs in and authenticates on Snapchat.

Step 10. Find a Snap to save to your device
Once Casper loads you will see a list of your recent Snaps. You can also open the menu by pressing ☰ to select any Story you have access to. Tap a Story to see all of the individual Snaps there.

Step 11. Tap a Snap to download it
So you can view it in Casper. The other person will not be notified.

Step 12. Tap the downloaded Snap to view it
You can view the Snap as many times as you want without using Replays.

Step 13. Press the Download button on an open Snap to save it
It will be added to the section Saved snaps from the menu, which will allow you to find it quickly whenever you want. The other user will still not be notified that you saved their Snap.

Step 14. Open menu (☰) and tap Saved Snaps to view all the Snaps you have saved
There you will find all your saved Snaps. They are also saved in the folder Saved snaps from the “io.casper.android” folder on your device.

Step 15. Check regularly for updates
It is very important that you keep Casper up to date to prevent your account from being locked out. If you plan to use Casper on a regular basis, you should monitor the Casper page to see if new versions are available.
Method 2 of 2: Jailbroken iPhone

Step 1. Jailbreak your iPhone
To be able to save Snaps on an iOS device, you need a jailbroken iPhone. Jailbreaking can be a difficult or even impossible process depending on the version of iOS you are using. Check out jailbreaking an iPhone to find out if your iPhone can be jailbroken and if so how.
If you can't jailbreak your iPhone because of the version of iOS you're using, you won't be able to save Snaps without notifying the person sending them to you

Step 2. Launch Cydia on your iPhone
Cydia is the jailbreak package manager that will let you find and download the Phantom Snapchat trick. You will find Cydia on your home screen once you jailbroken the device.

Step 3. Tap the Search tab which is located in the lower right corner
This will open the Cydia search.

Step 4. Search for Phantom
You should see a list of results. Phantom is available in the BigBoss directory, which is preconfigured on Cydia.

Step 5. Select Phantom developed CokePokes
This is an extension that will allow you to save Snaps without the sender being notified.
Phantom is available on iOS 8 and iOS 9

Step 6. Press the Install button which is located in the top right corner
This allows Phantom to be added to the installation queue.

Step 7. Press Confirm to start the installation
The change will be downloaded and installed on your iPhone, which may take a few minutes. Once the installation is complete, your home screen will reset.

Step 8. Launch Snapchat
The Phantom extension directly controls the Snapchat app. Launch Snapchat to see the new options.

Step 9. Open the Snap you want to save
You will be able to save any Snap directly from the Snap itself. Open the Snap you want to save to your device.

Step 10. Press the new Download button which is located at the bottom right of the opened Snap
This button was added by Phantom, it opens a new menu.

Step 11. Select Save to Photos to save the Snap without notifying the other person
The Snap will be saved in your iPhone's image gallery. You can do the same for any Snaps you like.

Step 12. Open the Snapchat settings menu to see the Phantom settings
You can adjust Phantom's settings from the Snapchat settings menu. Tap the ghost button on the Snapchat camera screen, then tap the gear button. You will see a new option allowing you to adjust the parameters of Phantom.
You can make Phantom automatically save all received Snaps and you can schedule it to save the Snaps to a password protected folder in iCloud instead of saving them to your image gallery

Step 13. Check regularly for Phantom updates
Phantom is regularly updated, usually every time Snapchat blocks it. If you think you are going to use it regularly, check daily for updates in Cydia.