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#11
Didn't read any of the above. Just saw the picture and it looks familiar.
I have PeerBlock on my computer, and it is the reason why this sometimes happen; I have to let it off its restrictions for a temporary amount of time, and it loads images.
If you don't have this program, then it is most likely some FireWall/AntiVirus program that you have installed that is doing this.
More complexly, your Router/Modem may have some restriction on it that causes this.