Yeah it's definitely not the kernel or the ROM or...anything. This may be much ado about nothing. I'm on the same page as Karl-some type of compression going on but after multiple pics I cant pinpoint a pattern.
It's not the kernel. Here are two pics taken 30 minutes apart. The first is 1.51MB taken with a modded kernel (8MP Standard resolution 4:3)
IMAG0051.jpg
and this is taken on the stock kernel and its SMALLER 1.08MB
IMAG0052.jpg
Heres even more proof (to me) that there is no issue.
One of my first pics taken, complete stock, unrooted. I know it was 8MP but it may have been in widescreen so really 6.7MP due to the different dimensions of widescreen. It's 1.73MB
IMAG0002.jpg
This pic is on OMJ v3.0 with a modded kernel (not sure which one) and again 8MP Widescreen and it's a lot closer to the "correct" size 2.14MB
IMAG0024.jpg
To my eye all the pics look fine.
I do not think/know if there is a correlation between file size and quality as much as there is between dimensions and quality. IMHO dimension is a much more important variable.
Hope that helps.