Although the SIG Pro params shows a directory for images, you can ignore that for K2.
All k2 uploads are saved to media/k2 then you will see the folders such as item, attachments etc.
This could be a server setup issue.
Check that media/k2 folders to see if the images have been uploaded.
If they have not been uploaded, then they will not be displayed.
There could be numerous reasons for this, so you might have to check your server settings.
Do a search in the forums, there are a host of other that have had similar issues that have resolved by changing some settings.
Simon
K2 Support
Check
simon.getk2.org for handy K2 guides