[Windows Phone 8 Development and Hacking] CreativeGamer03:
This thread is part of customizing the Windows Phone OS or ROM, which includes altering of the target files and no nothing else. Do not go sideways on this tutorial as you might brick your phone. PLEASE TAKE RESPONSIBILITY. I am not responsible to any damage caused by this tutorial. Also, do this if you want to personalize your device.

CUSTOMIZING THE OEM BOOT SPLASH IMAGE WITH SOMETHING HILARIOUS OR EPIC

What you need:

- Windows Phone Internals (for booting Windows Phone into Mass Storage Mode)

- Photo Editor <optional> (for editing the oem boot splash image. If you made one with as large as your phone's screen resolution, please disregard this)

- Administration Account (for DISKPART)

- CAUTIOUS MIND (of course)

- and a Windows Phone (obviously)

Procedure:

Getting Ready

1. Boot your Windows Phone into Mass Storage Mode. To do this, either shut down first your phone then boot it up whilst holding down the camera button (if any), or use Windows Phone Internals (https://wpinternals.org/) to boot into MSM manually. If you haven't unlocked the bootloader and enable root access yet, please do.

2. Using DISKPART, select the appropriate disk number from the list of disks (list disk) and do select partition 20 to select the target partition.

3. Then type in this command:

detail partition

This will show the default Partition Type ID. Save this GUID for a later step.

4. After saving to notepad or a sticky note, do:

set id=ebd0a0a2-b9e5-4433-87c0-68b6b72699c7 (to make it read-and-write-able)

5. To assign the drive with a letter:

assign

Now your done with PART 1! Proceed for more.

The Main Thing

1. On the file explorer, go to PLAT Drive. Then edit the two files, namely: boot1.bmp, boot2.bmp. Make sure the photo is as big as the default screen resolution of your device. (e.g. Nokia Lumia 520 = Screen Resolution: 480x800) If you made custom ones already, replace them with no problems.

P.S.: Mostly recommended: 32-bit bmp image export setting (on Photoshop).

2. Once done, proceed to the next stage. Make sure no other files is altered. If the image format is different, a System File Integrity error may occur when you boot up the device after this procedure, causing it to display a black screen without letting you to boot it normally.

File Info:

******[BOOT1.BMP]******
This is displayed or splashed when the device is booted up from powered off state.
******[BOOT2.BMP]******
This is displayed right after the first one in 0.1 second delay. It is also shown after the "Charging on Low Battery" screen when it has enough minimal power to boot up normally.

Packing Things Up

1. Go back to Command Prompt. Set the Partition Type ID back to default by pasting in back the GUID code you copied in Stage 1 step 3.

2. After these steps, finally reboot your device to exit Mass Storage Mode.

3. You will eventually see the result when it boots up. Voila!

General Questions:

My device boots into black screen. What to do?

A: Make sure the Partition has these information:

File System:	FAT12
Partition Type ID:	<the default GUID, not the GUID given here>
Partition Size:	8 MB

If not, please fix those problems yourself.

Can I use an animated GIF instead?

A: Impossible. It only accepts bitmap-still images, not animated ones. This is because it is on a BIOS environment (maybe?).