XX4 help file says:

But if you have text under the photo, this probably will not work well as the browser displays text in slightly different positions or size. In this case you can force the image to be output as a PNG image which will work correctly. To do this just give the photo a name 'PNG' using the "create new name" icon on the Selector Tool InfoBar.
Not for me it doesn't. Also help says:

If you rotate a photo on the page this is exported as a PNG image automatically.
Again no it doesn't, at least not for me, I always get a jpg. Does it work for anyone else?

I love the HTML export thing anyway, but transparent images over text would be divine.