Weird white block appearing over my images

A somewhat common issue that seems related to several different products, including php, java, and possibly imagemagick. It does not seem to generate any errors so it's difficult to debug.

Quick fix:
Reupload the image and check it got there correctly. If that fails, delete it and add it again.

It also seems to afflict slower systems more than faster systems so a processor upgrade might help correct the issue.
I have a personal and sneaking suspicion that this issue is related to the non threadsafe version of php either mashing shared ram or interrupting the processor during critical operations causing image upload corruption. It tends to be really bad on a slow system using IIS and the Java Upload applet or Gallery remote but I've noticed it with the Web Publishing Wizard as well.

I also noted less of an issue with graphicsmagick as a graphics package vs Imagemagick. If you are usign Linux it may be as easy as removing imagemagick and installing graphicsmagick in its place.

If you are not using a Linux box, think about switching. A debian box is very easy to setup and will host pages much faster and more efficiently than IIS. Linux is far and above a better OS for web hosting. It has a much better theology for application development and execution and uses RAM far more efficiently. In windows, file operatiosn tend to "grow" the system cache endlessely forcing a post to disk before new programs can load which certainly doesn't help web hosting where you have to load and unload small code a lot.

Hope that helps.