Once I installed this extension, it took me about six seconds to create a presentation based on a directory of graphics, one slide for each graphic.
Download the extension, don't unzip it, then choose Tools > Extension Manager as always to add it.
Then choose Tools > Addons > Create Photo Album.(If that doesn't show up, restart OpenOffice.)
Point to the directory where your graphics are. That's it. You get a presentation.
Only thing is, the randomly chosen slide transitions are a little annoying, so click the Slide Transitions item, select No Transition (or something you like), then click Apply to All Slides. And you can use that pane also to change the amount of time on each slide, or to switch it to manually going from one slide to another.