The 'dots' you see stuck all over parts are called alignment markers. Some scanners (usually hand helds) require these in order for the scanner to know where it and the part are in XYZ space. They can also be helpful if there isn't enough unique geometry between overlapping scans for proper registration - such as a smooth tube or large flat area. The dog & pony show you see with most hand held scanners - don't really show you the alignment markers or the process of removing them from the scan data. They can be a real pain in the butt for certain jobs and the software required (like the Geomagic software Stan shows) is around $15k(!) to sense, remove and heal the surface. Some scanner software has this ability built in.
Photogrammetry can be fun, but what you get is far from reliable. Even with a calibrated DSLR camera and ideal shooting techniques, the level of detail you can expect to capture is usually no more than 1 to 3 mm. Even with professional photogrammetry software, you'd be hard pressed to get results reliable enough to say that you have the ability to replicate something reliably with correct proportions and scale. However, for free form reliefs - particularly large ones or things that cannot be moved, PG can help at the very least, to get some base geometry/shapes that you can further develop/sculpt in software.
A few weeks ago I was called out to scan the ship's bell from the original USS NJ Battleship. Someone tried to capture the shape of the bell and lettering using photogrammetry, but came up short. None of the lettering (only .05 deep, with black paint and hand punched texture) showed up as 3D geometry - only photographic texture - so they called me out to 3D scan it. I felt bad for the guy who tried photogrammetry because I know it was a lot of work - only to be left frustrated.
At first glance, one would think it would be easy to just get the profile, spin it and add the lettering. However, this particular shape was not conducive to that because the lettering would have been stretched both radially and longitudinally - making it nearly impossible to get it correct. I call this compound polar distortion and anyone who has done extensive rotary indexer work will understand exactly what I mean.
Photogrammetry has its place - but it doesn't do so well for practical things you might cut on your CNC. Again - it can certainly be fun if you are just messing about (and not too serious/hard on yourself about the outcome)...
If you need something for real - just send it out and get it scanned. It's cheaper and better than anything you could do yourself.
High Definition 3D Laser Scanning www.IBILD.com