Usually we add to a project photos shot in 3:2 or 4:3 aspect ratio. By default, the project in PTE AV Studio has a slide aspect ratio of 16:9, and we see black bars around the images on a 16:9 monitor.
There are 4 options to make the images fill the entire slide (screen):
A. Click the Project Options button > Defaults tab. Tick the "Cover" option. Click the OK button.
Now all new images added to the Slide List or Timeline will occupy the entire slide (screen) without additional black bars.
This method requires the Pro version of PTE AV Studio.
B. Select one or more slides and click the Styles & Themes button. Browse Image Category > Image - Cover Style. Click the "Apply" button.
Please note that this style will remove all additional objects (text captions) from the affected slides.
C. Select one slide. Click the Objects and Animation button. Click your main image (usually the one selected by default) and press Alt+S (Option+S on Mac).
You can quickly switches between slides staying in the Objects and animation editor. Press F11/F12 or arrows buttons at the top-right corner of this window.
D. Select one slide. Click the Objects and Animation button. Click your main image.
On the Properties tab, tick the Aspect Crop checkbox. And select "16:9" from the drop-down menu. Or choose any other aspect ratio you want.