I'm also guessing that they're directly comparing the handwritten character to some version of the unicode character rather than with human attempts to draw the character. Human drawings are often quite different (more slanted, stylised etc.) than typeface characters. This is much more forgiveable though because assembling a good dataset for human drawn characters is hard (especially for any reasonable chunk of the unicode set).
(*this is fairly easy to do: just find some large source of typical unicode, like Wikipedia in all languages, and index them).
I don't know if that is the right metric for this sort of tool. I'd guess the use case is for trying to find infrequently encountered characters. It should probably try to detect your current locale, and then say eliminate all ASCII characters when you are suspected of speaking English, etc., since you are already aware of how to type a question mark.
Maybe we're training it?
Too bad about not supporting 漢字. The only half-decent IME pad is on Windows. Online ones (kanji.sljfaq.org) and Xorg ones (ibus-mozc) are just horrendously bad at detection. I usually have to resort to multi-radical lookups.
Sometimes it won't include one of the radicals that are clearly there, though. But this tool is frequently helpful to me when IME pads fail me, and stroke counts are fuzzy.
http://www.fileformat.info/info/unicode/char/search.htm
http://www.fileformat.info/info/unicode/block/index.htm
(I've added the above as search engines in Chrome with short mnemonics for the keyword.)
There's also:
http://unicode.johnholtripley.co.uk/ -- mobile unicode support tables
http://apps.timwhitlock.info/emoji/tables/unicode -- emoji :D
http://panmental.de/symbols/info.htm
and of course:
http://copypastecharacter.com/
Want more unicode resources? There's a list of other resources here:
http://joewlarson.com/blog/2014/01/01/useful-unicode-resourc...
javascript:(function(){var newcss="samp { font-family: Segoe UI Symbol; }";if("\v"=="v"){document.createStyleSheet().cssText=newcss}else{var tag=document.createElement("style");tag.type="text/css";document.getElementsByTagName("head")[0].appendChild(tag);tag[(typeof document.body.style.WebkitAppearance=="string")?"innerText":"innerHTML"]=newcss}})();Took me several tries to get # (regular ascii number sign - i.e. shift+3).
For example, tried drawing a somewhat joined 'TM' a couple times but no matches for 'Trademark symbol', however a way to manually input that unicode/name might provide the database with a positive match for the next user trying to find it.
edit: The primary problem here, I mean, is that if you don't know what the symbol looks like and want to see if it exists, you might not get hits the first time you try to draw, but it might not actually exist anyway.
For fun, I tried Eth ð, Thorn þ, and Hungarian ű, all of which it got, but not as the first choice. It did not find the Ing rune, which looks a bit like a < and > combined.