Easy to use scan app for linux simple-scan can be used for scanning on linux
Here is how to make it run with Optic Slim 2400+ scanner
Install sane
sudo apt-get install sane
Create scanner dir in sane shareed location:
sudo mkdir -p /usr/share/sane/gt68xx
Copy cis3R5B1.fw file to /usr/share/sane/gt68xx/
sudo cp cis3R5B1.fw usr/share/sane/gt68xx
Now open simple scan app - that's it !