I have always wondered if it's possible to make a homemade primitive photo sensor for capturing photos in an acceptable range and in low resolution using environmental light? I know that it's possible to use the mechanism of an optical mouse for scanning documents with very low resolutions, but it fails at longer distances than a few millimeters.
One option would be
- Mount a small photo-sensor on an X-Y carriage positioned on the focal plane of your "camera".
- The shutter would be left open permanently and the sensor stepped across each line in turn taking as many samples as you want to construct your image.
- An analog grey-scale reading could be taken at each point, shifted into memory and a grey-scale bitmap created from the results.
Figure 1: A single-pixel camera on a pan and tilt mechanism. Source: Arduining.com.