The Alphabet Detective Series is a great little alphabet book series that aims at teaching children the alphabet by engaging them in fun detective work.
In the Find the Hidden Letters books (of which there are four, a winter, spring, summer and autumn version), children are to find hidden letters in the pictures. E.g. it could be a tree shaped like a V or a signpost shaped like a T or something like that.
In the Find the Hidden Objects book version your child is supposed to find objects (starting with a specific letter) hidden somewhere in the pictures (which consist of beautiful art paintings or drawings that I have found online and that were in the public domain (copyright expired)).
All 5 books come in a PDF, epub and mobi/kindle version.