I'm currently running CyanogenMod 7.0.3 on my HTC Desire, and pictures copied to the SD card disappear!
If I copy an image from my computer to the phone using USB Mass Storage mode, it disappears as soon as the copy is finished.
Pictures taken with the Camera app disappear too.
Pictures copied with adb push some_pic.jpg /mnt/sdcard/DCIM/100MEDIA
don't show up in the Gallery app.
.nomedia
files usingfind
and found one in the card's root, but I suspect it's been recently added by a recent ROM Manager bug (I didn't take note of the file's creation date before deleting it)./mnt/sdcard/.nomedia
and/mnt/sdcard/DCIM/.thumbnails
and rebooted the phone, and the pictures are back in Gallery. Let's see for how long....nomedia
file away :) I added this as an answer, including some closer explanation -- so you might want to check and possibly even accept it, as it solved your issue.