I can help you with this, if required.
I have some ideas on how to implement this if you are interested.
So the only one`s not supported by OE are bmp, tif/tiff, tga, pcx, psd. Not sure if you can get size of flash files.
While most of these formats are not overly common (flash excluded) on the internet, they are used sometimes.
If you were going to add support I would highly recommend using the GFL library because it will save you the hassle of parsing them to get the size. The GFL library handles all these formats and many more.
Regarding Flash files - they do not have dimensions at all. Try to browse some SWF file (not inside a Web page) and you will see that it resizes with the browser window.