X mark hidden picture

Dear Sir/Madam:

I have windows Xp professional with sp2 installed and also all the recomended and custom updates are installed up-to-date but still when open few websites I am unable to see the pictures only X mark's are visible inside the rectangular or square boxes , i tired selecting the X mark and say show picture but still same problem as well for few websites i will get the following message in the internet explorer
 "Some pictures have been blocked to help prevent the sender from identifying your computer Click to download the pictures" if i click on this then i can see the picture but in some cases even i click iam not able to see the picture finally it only remains as X mark with unknown picture , please help me to resolve this .

Regards
D_wathi