4S, jailbroken, and this problem just started yesterday or the day before for me as well. I thought maybe it was BiteSMS, but an uninstall didn't fix it. Turning off all my WinterBoard themes didn't fix it either. Even the native Messages app won't open them.
Here's the odd thing...I figured out that it's not so much that it won't open them, but rather it won't display them. If I tap the little arrow in the bottom corner and then select save, the photo shows up in the Photos app. It just won't display the image within the Messages app (although it does display the preview in the chat thread.