Why pictures, loaded by me to forum disappear after some time?

I have recently posted several messages to forum with pictures, but pictures have then disappeared after approximately a day.

e.g.: look at my post from Wed, 2012-11-28 14:20 here:

http://www.planningplanet.com/forums/spider-project/529721/using-resource-skills-feature [1]

Or post from Tue, 2012-11-27 08:38 here:

http://www.planningplanet.com/forums/spider-project/530051/risk-analysis-spider [2]

At the same time I can see, that pictures, posted by others did not disappear.

What could I be going wrong?