How do I make older images in my /sdcard/DCIM folder show up in Gallery?
This behaviour is not uncommon, sadly.

I use SDrescan to fix it usually.

Here are some other questions targeting the same underlying problem:

The music player keeps displaying deleted songs. How do I remove them or refresh the library?
Picture Gallery Slow &amp; Won&#39;t Refresh on HTC G2 w Android 2.3 Gingerbread