Upload a picture here. (It should be 540x960 pixels. If it's not, it gets resized without preserving proportions.) It generates a .zip that you can flash in recovery.
Or pick one from the list at the bottom of this post.
You must be on hboot 1.06 or 1.09 for this to work. If you're not, here is how to downgrade your hboot.
If you're S-Off, this will work on any hboot version. If you're not, here is how to get S-Off.
Flashing a new boot splash does not get rid of the red "This build is for development only.." warning text. (Edit: Now that we have S-Off, you can edit out the warning text in the hboot image. I tried it. It works. But it's a dangerous thing to do if you don't do everything exactly correct.)
If you create one that you feel is especially nice, feel free to post it in this thread. ("Pics and zips please.")
/!\ So far there are (at least) 2 reports where the flashable zip did not work, but manually dd'ing the raw 565 file into mmcblk0p14 did work. If someone can point out what the update script in the zip does not do that is required to successfully flash the splash, I'd be very interested.
You can also get rid of the red warning text overlay. (If you're S-Off)
I modified a couple of hboots to edit out the warning text, and made flashable zips for them. See post #148. <-- You must be S-Off for this. If you're not you can get bricked.
(A side effect of flashing the 1.14.0004 hboot is that your ** TAMPERED ** flag is gone, even when flashing different ones afterwards.)
Original post, from before it was so easy...
If you have a 540x960px image, save/convert it to raw rgb565 (The resulting file should be 1036800 bytes.. 540x960x2) and dd it into /dev/block/mmcblk0p14.
I tested with this attached one. (That zip is not flashable. Just unzip it and dd the raw 565 file. You dont need to be in recovery, you can do it while booted.) I'm sure others can do better but this was good enough to see that it works, and I like a dark splash better than the light one.
You will still get the red 'This build is for development only' stuff overlaid tho.
That overlay text sits in mmcblk0p12:0xBD700 by the way but I dont dare poke into that partition.
Update 2012/7/19: See post #8 to make it flashable from recovery.
Update 2012/7/25: Looks like this will only for for hboot-1.06 and 1.09, not for 1.13 and up. (Unless you're S-Off)
Update 2012/9/20: Collected all boot splashes here.
Update 2012/10/1: Made a php thingy to generate flashable zips from a web form. See post #115.
Update 2013/1/2: Redid this post to point at the online zip generator.
Update 2013/2/22: Made some additions/edits regarding S-Off
Update 2013/2/23: Added some flashable edited hboots. See post #148.
Update 2013/3/16: Added fastboot-flashable zips, as it is now discouraged to flash hboot in recovery. See post #274
Update 2013/6/11: Minor php script update in the online generator because I added a version for the One-M7
Update 2013/11/22: Confirmed to work on VilleC2 as well.
Update 2014/05/31: Added support for the Desire X
Update 2014/07/15: Added support for the One M8
Update 2014/07/17: Hmmm... So it turns out that the zips for the M7 also work for the Butterfly S. I had no idea.