Why not use “Grid Technique” to put items in the picture to be memorized…!
If I want to use an image for ‘loci’,I just use the Grid Technique after I have familiarized myself with the image. I feel,it is the fastest way to use an image for storing/encoding memory.
For example,in the image of Monalisa below,I created a 3x3 grid. I put my items in each grid/square. And I can get 9 ‘loci’ like that instantly. I can put this image of Monalisa on the wall of my Memory Palace room. I can put other images on the wall with Monalisa,and each one will give me 9 loci. If I put four images on four walls of the room of my Memory Palace,then,I will get 36 loci(very fast)
Just my way…I use Grid extensively. And it is time consuming to find out and memorize the ‘loci’ in an image. So,I feel,Grid technique may be the fastest(and more effective) way to do things! 
