Hello Paulius,
to change the mouse cursor for the thumbnail images in the gallery module, add the following CSS code to a CSS file that gets loaded in your template:
(this example will change the mouse cursor to a crosshair when hovering a thumbnail image in our gallery module)
.extro-thumbnails a.emgallery img { cursor: crosshair; }
Changing the mouse cursor can be done for any HTML element, not only images.
For more information about the CSS cursor property, please see
here
Regards