Could you post the code?

Are you saying that after a postback, the control that displays the user's
picture doesn't update (to the new picture for example)?
This is probably an event sequencing problem. When doing a postback, you
need to look at the events that are called:

(summarized, not complete list:)
1) Page OnLoad
2) Controls' Page OnLoad
3) PostBack event

If you notice, your postback event handler, which is where I imagine you are
modifying the picture, is called after the control's page load. Therefore
your control is rendering the correct image, you just changed it AFTER the
control did it's processing.

To fix this, I suggest moving your control's PageLoad functionality to an
OnPreRender event handler instead of the OnLoad handler. This may have
further implications depending on your code though. But for simple custom
controls it doesn't.

HTH

Steve