I don't think these sort of things are actually that useful generally. Especially with claims like "three words in ten seconds" - do you really think that someone will in ten seconds learn these words long term?
I don't get the choice of image, either.
In addition, any serious learner will pick up kana early on, phonetic spellings aren't really that helpful.
Wow thank you for your feedback! It is very helpful.
1. I am not sure what you mean by "long-term." Visual association should help long-term memory.
2. I picked words starting with shi. So used the image of 'she', meaning a girl...
Thank you for your reply. I really appreciate it.
1. What material would you suggest for efficiently learning Japanese vocabulary? I could not find any.
2. I agree with your point about the sound 'she' but English approximation of sound is OK in my opinion.
For beginners, I would suggest a textbook, to which you can add online courses like Erin's Challenge, and if you use Anki or other flashcard programs, not just using Japanese word = English word but including a sentence in Japanese so you can see how it is used in practice.
Making up mnemonics is definitely a good way to help remember words and kanji, and in fact there are already many sites that offer such mnemonic lists, be it as text or as images. See KanjiDamage, Memrise, WaniKani etc. In fact, Memrise allows you to upload your own mnemonics for others to view.
However, teaching people only the pronunciation and not the writing (even if it's just kana) is not very useful. Also, when sharing your own mnemonics with others, you always run into the risk that they won't understand them - for example, I have no idea how the image in the first post is supposed to express jealousy. If anything, the girl looks like she's playing dead. (Maybe "jitto" - "motionless" would've been a better word to include)
Finally, learning Japanese is about more than just the vocabulary
Ever heard of the story of the tortoise and the hare?
The key to learning vocabulary, in my opinion, is repeated use in different contexts, over time. Seeing a word in a word-list/flashcard is one thing, but then reading/hearing it in an example dialogue or skit + using it yourself (doing drills/exercises) cements the information.
I personally find mnenomics in English for learning Japanese awkward. Maybe for the words that really trip you up, but very basic stuff like 下?
There are times when an English-based mnemonic (or other language) can be highly useful. 設定 actually sounds like "settings". 軍 is pronounced "gun" out of all things. The masu-stem of 滞る, とどこおり, can be split up into "todo" (as in, a to-do list) + こおり (ice) = putting the things you have to do on ice = delay. As soon as you realize these, you can be sure to never forget the word again.
Though I digress, it's not often you can make a mnemonic that's this straightforward. Most times they require some roundabout thinking.
The vocabulary I remember best are the words I encounter often. So words I read and write. Flash cards are just an extra boost, not my main way of memorizing, and if I'm getting enough exposure I don't need mnemonics to remember. I just see the word and know what it means.
Personally, I use a textbook, some good graded readers, and daily writings. All of this with a teacher (or one can use another knowledgeable critic, lots of people here do, I just prefer to have a teacher) to make sure I'm reading and writing correctly.
To me this is the difference between memorizing the multiplication tables vs. learning how to do math. I probably learn vocabulary more slowly, but what I know I know absolutely and immediately. For me this is key for reading and writing fluently. Mnemonics get in my way for fluency.
Are you making these for yourself? If so, I consider this a bad approach to the language, taking in account that I'm a very conservative person, I think sticking to more traditional learning methods would be more effective. If you want to insist in this flash-card style , instead of new isolated words, put small sentences from books, mangas, daily news, even sentences that you've translated/studied before, so that you have to pay more attention to them and make some effort to comprehend the grammar involved.
In my experience isolated kanji and vocabulary pieces did little to improve my grasp on the language.