These are not commonly seen in grocery stores or mall like 1D and 2D barcodes. Many manufacturing companies needed a barcoding system much like the UPC barcodes used in stores to track purchases and store product information. These manufacturing companies could not just use a regular barcode that is normally printed on paper or a sticker, because of the high temperatures, chemicals, and solvents that would easily destroy a barcode. To solve this problem they discovered a new way to track their parts in the manufacturing system by using 3D barcodes.
As I explained earlier in the article on the difference in dimensions, three dimensional objects must have thickness and must be measurable on the x, y, and z-axis. Therefore a 3D barcode is usually engraved on a product or applied on a product so that the barcode has depth and thickness. Check out this picture of a 3D barcode. Unlike 1D and 2D barcodes, the bars in a 3D barcode are read by a scanner that reads the differences in the height of each line. Other types of barcodes are read by the variances in reflected light as the light scans the code. The 3D barcode scanner uses a laser that calculates the height of the barcodes lines based on the distance and time it takes for the laser to read it. As you can see from the different dimensions involved in different type of barcode making and the formula involved in reading 3D barcodes, there is a lot of basic physics knowledge involved in their creation and decoding. Once the scanner scans the 3D barcode the result read by the height of the lines is interpreted.
The labeling of parts with 3D barcodes is called direct part marketing or DPM. A direct pat mark barcode reader contains a laser like the ones that are contained in home and office scanners that scan pictures or documents in a computer. DPM readers only read the height variances of the barcode, therefore there is no need to make the barcode black and white as most other barcodes are. Those types of scanners normally read the white space between the barcode lines to decode the barcode.
This is an interesting, but older article on 3D barcode technology being used to identify stolen valuables: http://www.newscientist.com/article/dn7756-3d-barcodes-to-identify-stolen-valuables.html . It talks about placing microscopic 3D barcodes on valuable works of art, jewels, and other precious items, which can then identify them if they are even stolen. A electron-beam lithograph drills into the plastic face of the microscopic square which will be the future 3D code. The square can then be placed on an item using adhesive or woven onto items such as the canvas of paintings. I didn't find any information on whether or not this technology is currently being used for this purpose (the article was written in 2005), but it's definitely an interesting idea. I'm wondering if people could use 2D barcodes to keep track of certain valuables or even have them printed on their bank checks.
3D barcodes are actually very similar to 2D QR codes, since QR codes were first used to track vehicles in the manufacturing process in Japan. Now they are used in the US for marketing and customization purposes. I doubt 3D barcodes will ever move into the marketing arena, but it's interesting to know how they are used and what they are all about. When I first heard about 3D barcodes, I honestly pictured a QR code that was holographic; I was completely wrong. So while probably stuck in the manufacturing industry, 3D barcodes show another way that barcodes have helped make life much easier for people.