There's a frog on my blog!
Those of us who know about third party templates know what's up, here. Given the right browser, you can find the problem, in a couple minutes.
Some third party template providers use separate, third party image hosting services, for serving the graphics used by their templates.
Some of the image hosting services, unfortunately, limit their bandwidth. When a given image, that they are serving, exceeds a given amount of bandwidth in a day, or maybe a month, they stop serving the image - maybe the background or another decoration - and they replace it with their logo.
One of these "replacement" logos is the well known Imageshack / PhotoBucket Frog.
If your blog uses one of the more popular templates, provided by the third party service, your readers will find out about it - and you may find out from them.
Why is your blog so plain - and why are there frogs all over the face?And there is your blog - with no background, and with the frog images.
If you have Firefox, you can use the Media tab in the Tools - "Page Info" wizard. The Media tab displays a quick inventory of all images used, in any web page. Each image is represented by a URL, and a thumbnail. Just open the Media tab, with your blog (and the frogs) displayed, and scan down the list. When you see the frog, look at the URL - and there's the source of your problem.
Then pick another template - maybe an up to date Blogger template - and make your blog pretty, again.