Adding a photo directly to iPhone disk I tried to add a picture in the folder /User/Media/DCIM/100APPLE/ (the same as /private/var/mobile/DCIM/100APPLE/), but it doesn't show up in the Camera Roll.

How can we make it appear?
It's an iPhone 3G running iOS 4.3.1.
Following the advice in this forum thread, I've deleted the files (after backing up to the computer):


/User/Media/PhotoData/com.apple.photos.caches_metadata.plist 
/User/Media/PhotoData/Photos.sqlite  
/User/Media/PhotoData/PhotosAux.sqlite


After opening the Photos app again, it rebuilds the Library:


  


It's important to use the pattern IMG_0000.ext for the pictures file names:


0000 being numeric ID of our choosing
.ext is a JPG or PNG extension
we can add letters after the numeric ID to prevent conflicts with the device ID counter, ie, IMG_0041b.png, IMG_0041c.png, IMG_0041d.png.