There are several compounds which are sensitive to light that do not contain silver; the Cyanotype rocess comes to mind. These have not been used I think mostly because they are relatievly insensitive (relative to AgX) and are normally only sensitive to the UV spectrum. The article you post notes that TiO2 is higly reactive under light- So the TiO2 appear to be a redox catalyst under certainlighting conditions, the article states that the compound could also be doped, dyed, or otherwise to also be reactive under the visible spectrum.

I've heard of no TiO2 photographic processes, but if Titanium is such a strong catalyst when exposed to light, perhaps the trick is to use it as a catalyst to oxidise some other compound intermingled in whatever coating we're using as the "film". In otherwords, when the light comes through the lens and hits the coating, it activates the TiO2 catalyst which reduces or oxidies whatever nearby compound which would actaully form the image.

In any case, I think the cost of developing this solution as an alternative to a silver based emulsion would probably be the equivalent of many, many kilograms of AgNo3. Also, i'm guessing that it still would not equal the speed or spectrral sensitivity of AgX, but then again - I'm not a chemist, nor even a very good photographer.