Every time I want to place an image near another in inkscape, is trying to position it close to one of its corner. I could avoid this using the Shift key, but how can I disable that feature so I don't need to press the shift key which is annoying.
That feature is called snapping.
View → Show/Hide → Snap Controls Bar gives you a control bar whose first button allows you to deactivate snapping. The bar also allows you to activate and deactivate specific types of snapping. The one that annoys you sounds like Snap to bounding box corners.
You can also toggle snapping with the % key.
In older versions of Inkscape, you can also disable snapping with View → Snap.