How to differentiate between transparent_background and white_background?

Since picture with transparent background on Danbooru will also use a white background, is there any way to tell these two types of background apart?

The only way I know is to click the link by "Size" in the post information to view the raw image. I'm not sure how it will show up in different browsers, but in Firefox a transparent background will appear gray when viewed this way, while a white background is still white. Also, if the link goes to a JPG you can automatically assume it's not transparent because the JPG format doesn't support transparency.

Well a transparent background will only be present with certain image formats, so if the image isn't a PNG or GIF then it's pretty much guaranteed to not have a transparent background.

In chrome (windows) you can click and drag the image and it'll show a thumbnail of the image with the mouse pointer. An image with a white background will show up as having the background (example) while a transparent background image will not show a background (example). Sort of works in Firefox (although the white background is much harder to see), and doesn't work in IE.

Thanks fossilnix and NWF Renim for your help. Actually, I have already tried NWF Renim's method before. However, many of the posts with transparent_background tag actually show a background was making me confused.

Do you perhaps have it so that images are resized in your settings? The resized images are JPEG, so they won't have a transparent background.

Ah I see. I didn't know that the resized images also automatically convert to another format. Thanks.
I think you should add this information to the transparent_background wiki to help other users.

Now this is a little technical, but create yourself a bookmark in your browser to any random thing. This page, even. Open it up to edit it, and change the URL/Address of the bookmark to this:

javascript:document.getElementById("image").style.backgroundColor="red";void(0)

When viewing an image, clicking this bookmark will leave you on the image's page but will turn any transparent element a glaring red. Dunno if there are any browser incompatibilities, but it works in Firefox at least. Being basic javascript it should work fine.