Disappearing Photos

The last time I posted to my blog I noticed that some of my photos had disappeared, leaving in their places little boxes with red x's in them. The funny thing is that when I looked at the html, the code for the picture was still there, and all the missing photos are still in Picasa. So I went through my entire blog and fixed everything. This evening when I checked my blog, darned if there aren't pictures missing again. How in the world could they just go missing, when I haven't changed anything since yesterday? Seems to me I remember seeing something about this before, but wouldn't you know I have no idea where I saw it. If anyone has a clue why this might be happening, I'd sure appreciate it if you'd email me.