This is a game that is kind of similar to the 80's and 90's TV show Classic Concentration. The presentation consists of 99 small squares with a picture that is behind all of the squares. The picture can be changed depending on what the teacher wants to put in the background. This game requires that the teacher has a list of questions ready for the students to answer individually or in teams.
Here is how I play the game: I separate the class into teams with about 3 to 5 students in each group. I usually prepare a set of questions for each numbered box that is in the presentation (99 questions). These questions can be review questions from whatever unit/chapter the students are currently studying. I understand that is a lot of questions to have and the teacher can adapt and repeat questions if they want or think on the fly for questions if you don't have time to prepare 99 questions. So team 1 will select a number from 1 to 99 (but it has to be a number that they can see), and then the teacher will read the corresponding question for that number. If the group answers the question correctly, the teacher deletes the box from the presentation and reveals part of the picture in the background. That same group can have one opportunity to guess what the background picture is. If the group answers incorrectly, the box stays there and the teacher goes to the next team. If it's correct, they win the game. If it's not correct, the teacher goes to the next group to select a number. The next group can choose the same number or a completely different number. This cycles through the students faster and gives all the students more playing time.
99 boxes is a lot of boxes and the teacher can eliminate some of the boxes before the game begins if they want the game to go faster for the students. In order to change the background picture in the game, the teacher will need to just move some of the boxes to the side so that they can 'select' the background picture. Once the background picture is 'selected', delete the picture. Then find a picture that you want to use and copy and paste it into the presentation. Adjust the size of the picture so that it fits square into the presentation slide. The image will be 'in front of' all the boxes, so you will need to "right click" on the image and then select the option "send to back" so that it is behind all of the boxes and the students can't see the picture.
I understand that it is not necessarily user friendly to change the picture, but once you figure it out, it is very easy to do. If you have any questions, please feel free to message me and I will be very happy to help.