This is what the documentation says:
Image Show GK4 – a slideshow module for Joomla! (2.5/3.x), using it you can create an attractive slideshow on a site which include various images and article fragments or texts defined by a user. You can enable Random slides order or use manual order. Module is mobile compatible & responsive design (adapts the image to the width of the container) and it have multilingual support (read more). For upgrade to new version please reinstall the module.
Options Tab – ‘ADVANCED OPTIONS’
The “Generate thumbnails” – if this option is disabled, the original images are used in the slideshow. Disabling thumbnails is working with styles using one thumbnail per image.
The “Use style CSS” – you can disable loading the selected style CSS code if you’re using template which was designed to use the selected style.
The “Random slides order” – allows you to enable random slides order if you need display slides in different order on each user visit. We recommend to enable it when you have more slides – on smaller amount of slides i.e. 2 slides, the randomization effect is less visible.