If you ever wondered why color printers with a separate black ink tank won't print a black and white document when it's low on color -- it's because they have to print the secret yellow dots for fingerprinting purposes and need the color ink to do so.
First, the reason inkjet printers use color ink for monochrome documents is pretty well known. While there is no doubt a degree of "profit optimization," there's a printing benefit to doing so. Most inkjet printers, because of the properties of the ink used, cannot produce very good blacks with only their black ink. It's standard to use some magenta and blue to 'deepen' the black which produces a subjectively better result. On many printers you can toggle this off, either on the printer or in the print driver. But, and here's where the profit optimization comes back, on a lot of cheaper printers especially you can't (although this might have more to do with the general lack of configurability of inexpensive printers). This technique is unnecessary for laser printers because of their different properties (toner is an opaque material bonded to the surface of the paper; ink is a liquid with a degree of transparency that is absorbed by the paper).
There's also an argument made by inkjet manufacturers that cycling the color cartridge is important to keeping the print head ready for use, although I don't think it's really that big of a motive since with some firmware work they could just run the cleaning cycle on the color cartridge for each print job (although, once again, a lot of this comes down to cheap printers being built around commodity controllers with very little configurability or intelligence in general).
Second, MIC-type dot markings are associated only with laser printers. The concept was developed within the laser printer industry and does not work as well on inkjets due to the higher level of bleed and poorer halftoning of very faint colors. I am not aware of any inkjet printers that print these types of dots; I would not be surprised to learn that there are a handful (particularly in the higher-end photographic market) but it's certainly not common. The EFF, for example, says that no inkjet printers do so. There's probably not much value to printing tracking dots anyway, because inkjet output is usually more obviously different from offset printing than laser (poorer color saturation and density), which makes inkjets unappealing for counterfeiting. There are, of course, a whole different class of "giclee" printers with excellent output quality (is HP Indigo still king?) but they're specialty devices and tracking dots only appear on consumer and office equipment.
There's a couple reasons that I know of, plus I suspect it may be cheaper for the manufacturer. One is that the media type selection in the printer driver (especially glossy vs. matte) changes the ink composition used for black, and you wouldn't have the ability to adjust that if it was premixed. Another is that "automatic" use of color inks for black is an RGB thing; when printing CMYK the same thing is done but it's actually part of the original data. That is, a "deep" black in a CMYK image will have non-zero CMY. Another way to put this is that the whole "we have to use color ink to produce black" is basically an artifact of a mapping problem between how RGB additive-color and CMYK subtractive-color look for black. If you prepare a CMYK graphic you can put down a sample of "100% black" or CMYK 0,0,0,100 and whatever your editing tool considers "black," like CMYK 60,40,40,100, and you'll find that they look quite different printed. But people working in the CMYK space expect to be able to control that to their preferences; people printing documents get it done automatically as a convenience.
Photo-quality inkjet printers sometimes use two different black cartridges, I'm not sure what exactly goes into the composition of the two. Art reproduction inkjet printers (giclee) can use 10, 11, even 12 different pigments to get optimum reproduction across the whole gamut. It gets very technical.
> "Most inkjet printers, because of the properties of the ink used, cannot produce very good blacks with only their black ink."
Many inkjets solve this by using two different black inks. One which is the K in the four CMYK "dye inks" for printing photos etc, and another "pigment black" for printing purely B&W text etc.
For most modern inkjet printers, there's a simple reason: there must be ink inside the printhead at all times[1] or some of the nozzles will dry out and clog.
Solution/hack: buy one of those ink cartridge refill kits, but put black ink in the yellow cartridge. That way when you want to see the dots they should come up nice and clear?
Obviously this is not going to work out well if you actually print in colour.
Yep. Last time I thought it'd make sense to have a printer, cause I was printing lots of stuff for a wedding, it ran out of ink oddly quickly then broke soon after I refilled it. Also jammed a lot and wasn't easy to get the right drivers for it.
I forget what I spent, maybe $150 by the end and 4 hours of dealing with it. Never again.
The ink cartridges that come with the printer aren't full, and have never been as far as I can remember. That's one of the reasons a cheap printer costs as little as a set of ink for the same printer (the other obviously being the "give away the razor, sell the blades" business model employed)
Where I live, every 7-11 has an office copier/printer/scanner machine that also does photo printing you can use for a few cents. That's been good enough for my twice-a-year printing needs. It even comes loaded with sticker paper so you can print out custom stickers, pretty fun.
Well, yes. But the OP was suggesting/suspecting his printer prints security dots even when printing in B&W. This could be a good way to reveal them for analysis purposes.
I've looked into it before and I didn't find anything suggesting that it's a law. It appears to be willful collaboration with the feds and other nation states, possibly to avoid the attention of regulators, but it's all done in secret so there's not a ton of info.
Along similar lines, scanners and commercial software packages like Photoshop attempt to detect EURion dots and the digital watermarking that replaced it in currency. Obviously open source software has no such thing because it would be pointless, and it's not illegal that it doesn't.
For whatever reason, these antifeatures seem to also be missing from commercial digital cameras.
> Is this a federal (US) mandate or a law in any other country?
No, its a backdoor regulation in the US (probably using the threat of actual regulation premised on controlling counterfeiting to get firms onboard) via agreements from manufacturers to act without regulation.
Strictly speaking, no such law exists. My understanding is that it’s a request from the secret service that all of the printer manufacturers have agreed to comply with for counterfeiting reasons.
If you ever wondered why color printers with a separate black ink tank won't print a black and white document when it's low on color -- it's because they have to print the secret yellow dots for fingerprinting purposes and need the color ink to do so.