Apps are getting better all the time though, and the good ones let you correct a wrong ID so the next person's photo gets a better answer. A used guide from 1998 doesn't update when taxonomy changes, and half the trilliums got renamed since then anyway, so you could be learning names that are out of date. Nobody says you have to pick one forever, use the app to get you in the ballpark and the book to slow down and study the details. The real problem with the apps is lazy use, not the tool itself, and a $12 book teaches you nothing if you just flip to the picture and move on. Also not for nothing, some of us have bad eyes or shaky hands and a camera gets us further than squinting at a key at dusk.