How to verify if two images have the same object/content?
I am no expert, but I would like to give some pointers which could help you to solve. 


Regarding the method you have mentioned/used, is for image registering/stitching. You are interpreting the results wrong. Calculating the percentage of feature match is not the intention of inliers, rather computing corresponding feature points in both images which could be used for image registering/stitching. Inlier is the feature point for which the algorithm has found a corresponding feature point in the other image. Feature points for which the algorithm has not founda match are called outliers. More inliers, better the match. Keep in mind, the algorithm can sometimes match some feature points of completely unrelated images(try running your method on two unrelated images) 
Can you use the method you have mentioned to solve your problem ?. 
Yes,You can use number of inliers for each image in the database and decide the one that has the highest number of inliers as the match. You can have a minimum count of inliers to be present, in case the picture of a video-game doesnt exist in your database. 
Other ways/methods which you could explore to solve this. 


Explore more on the features you can use. SURF does well for some applications, for some it doesnt work well. You have to choose based on your data (image database). You can check with SIFT, and also color histogram as features. 
You can check bag of words for image search. (check this)
Whenever you add a new game to database, some algorithm(eg - bag of words) need the code book to be recomputed everytime you add a new image to database, so choose the algorithm wisely , coz as the image database gets bigger, the cost of computing  increases. 
Also think in lines where scale of the images differ(i.e image is database and search query image) Some features like SURF/SIFT are scale invariant, if you choose to use any other, keep this in mind. 



These points might help you in deciding and I hope I did not complicate your life :)