Images Disappearing (Randomly) 404 Error

Hello everyone,
I am hoping someone can help me.

When I post images to my wordpress blog the images display correctly. But recently older image-links have been ‘braking’ unexpectedly (randomly) and then return a 404 error. See:

http://jonathanauch.com/potd/picture-of-the-day-43/

http://jonathanauch.com/potd/picture-of-the-day-36/

http://jonathanauch.com/potd/picture-of-the-day-35/

I have not deleted any images from the media library so I do not know what could be causing this. It seems like wordpress is resigning the location of the images after I post them, but I don’t know how to correct this.

Thanks for any help you can provide.

All the best,
Jonathan