So I think this is a bit tricky, but just to be clear, it sounds like you already have a working Raspberry Pi and an image of Raspbian on an SD card. You have an image of some software that you want Raspbian to utilize and mount as a readable drive.
Looking at the site that you sent, there is a readme text file that you probably should also use and leverage for this. It doesn't mention anything about needing to download some separate software and installing it that way. SO the image you have I think is the standard Raspbian Jessie image with some references to this project, possibly a slightly custom distro for your purposes.
If you have that same file that is mentioned at the top as an image, I would go ahead and put that on a SD Card as you would with the Raspbian distro per the instructions on the RapsberryPi.org website. Then this SD card will replace the current one you probably have.
You may have some other software or other configurations on the original SD card or only have 1 SD card, so it might be wise to try to back up that data, and then possibly overwrite that SD card with the new image and follow the instructions in the ReadMe file / link above.
However, if you still have an image file that you need mounted and need to read from to install some software on it, I think the following steps might help.
The first thing is you need to run fdisk to find some general info of the image.
fdisk -l /path/to/image
Then you need to run the mount command based on the size of that image
mount -o loop,offset=65536 NewStuff.img /mnt/tmp
This should give you a mounted image of what you are looking for.