To answer the first question, Vidtionary is for anyone who is studying or teaching English. While it may seem that the largest market for visual language-learning aids is children, we think visuals are important for language learners of all ages. Vidtionary can be utilized by native speakers of English and ESL/EAL (English as a Second/Another Language) learners alike. Moreover, speech therapists may find it to be a useful tool.
In addition to language learners, anyone with an interest in visual literacy, such as graphic designers, may take interest in Vidtionary.