Hello,
i' am using K2 v2.5.7 and i'm looking for a way to have the images in category view floating left BUT the item view image i want to be in the center.
Is that possible?
Thank you Very much
Happy new year - Καλή Χρονιά!

Certainly it is possible.

You'll need to create a copy of the default template and tweak category_item.php &/or item.php

Use K2 categories template setting to pick up your custom template.

Quick & dirty example below is custom to my site. But should give you an idea of how to go about it.