dude! , I've had a brilliant idea! I used to play a game named tuby, its also a fitness game that is controled by camera, and it also had jump detection, only a pretty good one The way they did it is that they had a full body tracking, and they put an horizontal red line on the screen a bit above the legs and if it detected that the legs have touched that line it counted that as jump, then it deactivated(with a few milisecond delay) until it detected the leg again then it counted it as landed
Here its even more simple! , you can leave it as face detection, the only thing you need to change is that when the game is launched it will give you a 10 seconds countdown, in which the player will pick it preferred position and distance from the camera, stand up with his back and neck straight, and wait, once the timer is finished a red horizontal line will appear a bit above the face detection Square and a bit above that another line, and those will stretch from one side of the screen to another
from there its very simple, when it detect that the sqare have touched the bottom line it will wait a few miliscond to check if the sqare is going to touch the upper line, if it did not then it will initiate a small jump, if it did, then it will initiate a big jump(of course from the moment its initiated it will deactivate for a small time window to avoid duplicates until the player land)
and BOOM , jump detection problem solved!
and it has so much potential, you can even do the same with three lines to count as small medium and big jumps, or even more, the possibilities are almost endless (and if one of the line doesnt fit in screen then it will tell the player to back away a bit from the camra) but you don't have to if you are absolutely sure that with the small and big jump alone the game is really beatable , but it will be cool, think about it, your game will have more optains and control over the jumps then jump king itself!
You can even easily add an option for *multiplayers* by still using face detection, only player 1 will have the green sqaure and player 2 will have a blue square, the lines are decided by which sqare is higher(and if the other player is really a shorty and cant reach the upper line he can move a bit forward then he sould have no problem) then when the green square touches the line player one will jump, when blue sqare touches the line player 2 will jump and then the game will become a competition who gets to the top faster will be much more interesting and engaging
In short as I was saying this game has so much potential and can even be much better then the original jump king if you just put a bit of time to it I hope to hear from you soon, don't abandone this goldmine