Kindle Screen Saver Hack for all 2.x, 3.x & 4.x Kindles
Many thanks to clarknova (screen saver hack), porkupan (jailbreak hack) and NiLuJe (revised jailbreak and screen saver hacks).
Note: Amazon does not support 3rd party hacks and may void your warranty should anything go wrong. Exercise caution and use at your own risk. Only the user will be responsible for the results (good or bad).
Please visit NiLuJe's Fonts & ScreenSavers hacks for Kindles thread on MobileRead. This is the jailbreak and screen saver hack I will be describing.
WARNING: Use at your own risk! This is an UNOFFICIAL update to allow custom Kindle Screen Savers. This file is NOT from Amazon.com and any harm it causes your Kindle will be your own fault.
 Which Kindle Do You Have
And for other devices, check the Menu > Settings page.
Kindle DX Graphite: Serial no. prefix B009
Kindle 3 3G US: Serial no. prefix B006
Kindle 3 WiFi: Serial no. prefix B008
Kindle 3 3G UK: Serial no. prefix B00A
Kindle 4: Serial no. prefix B00E & B023
NOTE to non-US users: UK doesn't necessarily mean Europe, you may very well end up with a B006 model, depending on your country.
 How to install the Jailbreak Hack
Note for Kindle 4 Users:
Please skip this section and refer to the Wiki instead.
1) Download and unzip the kindle-jailbreak-0.12.N.zip file. [Note: If you have used the jailbreak previously on your Kindle (when installing the font hack), there is no need to re-install it].
Note for Kindle 3.0.x, 3.1.x & 3.2 Users:
Please use the file corresponding to your kindle model suffixed by -3.0-to-3.2, the other one won't work on these older FW versions, while this one won't work on newer FW versions. Check your Settings page if you're unsure of what FW your Kindle is running.
"Update_jailbreak_0.12.N_k2_install.bin" - Kindle 2 US "Update_jailbreak_0.12.N_k2i_install.bin" - Kindle 2 International "Update_jailbreak_0.12.N_dx_install.bin" - Kindle DX US "Update_jailbreak_0.12.N_dxi_install.bin" - Kindle DX International "Update_jailbreak_0.12.N_dxg_install.bin" - Kindle DX Graphite "Update_jailbreak_0.12.N_k3g_install.bin" - Kindle 3 3G US "Update_jailbreak_0.12.N_k3w_install.bin" - Kindle 3 WiFi "Update_jailbreak_0.12.N_k3gb_install.bin" - Kindle 3 3G UK "Update_jailbreak_0.12.N_k3g-3.0-to-3.2_install.bin" - Kindle 3 3G US (Only if running FW <= 3.2.0) "Update_jailbreak_0.12.N_k3w-3.0-to-3.2_install.bin" - Kindle 3 WiFi (Only if running FW <= 3.2.0) "Update_jailbreak_0.12.N_k3gb-3.0-to-3.2_install.bin" - Kindle 3 3G UK (Only if running FW <= 3.2.0)
2) Attach your Kindle to a computer using the USB cable. Copy the appropriate jailbreak bin file to the root of your Kindle.
3) Safely eject your Kindle from your computer. To update your Kindle with jailbreak bin from the home page, click Menu > Settings > Menu > Update Your Kindle. If "Update Your Kindle" is grayed out, you either did not put the bin file in the root folder or used the wrong file for your Kindle.
On FW 2.x only, the jailbreak update process will FAIL (with a U006 error in the lower left corner of the screen) but that's okay, it's supposed to. :)
To remove the jailbreak (if you somehow want to get rid of it... There's no practical reason to do this though ;)) use the same process described substituting the appropriate "uninstall" bin file.
 How to install the Screen Saver Hack (Does Not Work For Kindles With Special Offers)
1) Download and unzip the kindle-ss-0.43.N.zip file.
2) Attach your Kindle to a computer using the USB cable.
3) Copy the appropriate ss bin file to the root of your Kindle along with the "linkss" folder found inside the "src" folder.
"Update_ss_0.43.N_k2_install.bin" - K2 US "Update_ss_0.43.N_k2i_install.bin" - K2 International "Update_ss_0.43.N_dx_install.bin" - Kindle DX US "Update_ss_0.43.N_dxi_install.bin" - Kindle DX International "Update_ss_0.43.N_dxg_install.bin" - Kindle DX Graphite "Update_ss_0.43.N_k3g_install.bin" - Kindle 3 3G US "Update_ss_0.43.N_k3w_install.bin" - Kindle 3 WiFi "Update_ss_0.43.N_k3gb_install.bin" - Kindle 3 3G UK "Update_ss_0.43.N_k4_install.bin" - Kindle 4
5) Place your 600x800 (824x1200 if you have a DX) image files (png or jpeg) into the "linkss/screensavers" folder.
5b) If you want to randomize (at boot) the order in which your screensavers will appear, drop a blank "random" file in the "linkss" folder. (By copying and renaming the existing "autoreboot" blank file, for example)
5c) If you want to shuffle your screensavers each time an autoreboot is triggered, drop a blank "shuffle" file in the "linkss" folder. (By copying and renaming the existing "autoreboot" blank file, for example)
6) Safely eject your Kindle from your computer. To apply the update, on your Kindle Home screen, click Menu > Settings > Menu > Update Your Kindle. If "Update Your Kindle" is grayed out, you either did not put the bin file in the root folder or used the wrong file for your Kindle model.
Anytime you want to change your screen saver images just drop a blank "reboot" file in the "linkss" folder (or in the "linkfonts" folder if you also have the Fonts Hack installed) after you've made your changes and you'll be good to go.
To remove the screen saver hack, just copy the appropriate "uninstall" bin file to the root of your Kindle and update. Note that, since the v0.6.N, you shouldn't have to deactivate/uninstall it in order to be able to install official Amazon updates!
 How to Update the Screen Saver Hack
First of all, no need to touch the jailbreak again. You already installed it the first time you installed hacks. Just forget about it now ;).
Next, no need to run the Update_*_uninstall.bin update, ever. (except in some very specific cases, like if you're updating from another screen saver hack [in which case you should use the original uninstaller for your hack, and not the one found here]).
Then, you can apply the latest Update_*_install.bin update.
After that, to make sure everything's in order, do a full Restart of your Kindle, and you'll be good to go.
Basically, just do a full install of the hack like described here, and then restart your Kindle (Menu > Settings > Menu > Restart).