Infopath Picture Control Problem?

[王圣柱]

Hi:
I have a form that has embedded pictures(JPG format). It stores these
internally as base64-encoded xml. when I extract these pictures throug my
programm then save them, some pictures are changed,but some are not:

the attributes of picture has been changed:

first picture:
resolution: 800*1067----->864*1152
size: 655K ----->157K

sencond picture:
resolution: 2816*2112----->1152*864
size: 1.2Mb ----->90K

third picture(this not change):
resolution: 2048*1536----->2048*1536
size: 2.12Mb ----->2.12Mb

I find that InfoPath causes these changs,why??
how to solve the problem??

any tips for this would be appreciate

thanks in advance