LibreOffice Impress has a useful feature to export the slides of a presentation to PDF. However, if you have animated images in your slides, these animations are not exported to PDF. This is partly because most types of animations cannot be rendered in PDF as pages. However, the most common animation is for images to appear or disappear on mouse click. It should be possible to support these animations in PDF.
The ExpandAnimations extension can be used to export the appear-disappear animations in a LibreOffice Impress presentation to PDF. The download link for the oxt extension file can be found at its Github page. Double-click the file to install the extension using LibreOffice. Once installed, you can export any presentation open in Impress by using Tools > Add-ons > Expand animations
Tried with: ExpandAnimations 0.2, LibreOffice 18.104.22.168 and Ubuntu 12.04 LTS