Illustrator doesn't store the "original size" of embedded raster images. When you embed it, it is what it is: a given number of pixels scaled to its current size. You can see this expressed as pixel counts and ppi in (of all places) the Document Info palette, if you select Selection Only and Embedded Images from the flyout menu.
In the Links Palette, you can select Link Information from the flyout menu, and see the "scale" represented as a percentage. This is always relative to 72 ppi, so you have to tediously do the math and transform it accordingly to make it what Illustrator considers "100%" (72 ppi).
(Isn't this convenient? Isn't this intuitive? Worst-of-class interface among all vector drawing programs.)
Save the AI file as a PDF (Illustrator Default preset will do fine.)
Open in Acrobat.
When the photos are scaled you should be able to select them and Object>Transform>Scale and insert 200% (Uniform).
@JET: thanks man. You just saved me a couple hours of tedious work and headache. ROCK.
@Jacob: the scale function doesn't remember the original scale of any given object, so I were to simply scale everything to 200%, it would be 200% of the current scale which would give me anything like 198% to 174% to 208% etc.... but thanks for responding.
I would like to improve on James’s advice. Yes, save as PDF, but don’t use the defaults. The default values resample and use lossy compression. Start with the default, but turn off downsampling and compression, or use ZIP. Also, in the Output tab, turn Color Conversion to No Conversion.
You can then either do as James says and save all images from Acrobat, or you can open the PDF in Photoshop. Instead of opening a page, you can open an embedded image.
Edit: I just did this to check my terminology (correct) and discovered that the Illustrator Default for Illustrator 14 is just what I said, so James is correct for that version at least.