Conclusion
LibreOffice and Microsoft Office both have numerous graphics that come pre-installed. The suites do not make them available to all of their applications. In LibreOffice, Writer, Calc, Impress, and Draw have the Gallery, while it is absent from Base and Math. For Microsoft, the Icons are available to Word, Excel, and PowerPoint. Neither Publisher nor Access have the Icons.
Microsoft has more images than LibreOffice and more categories, but they are only black. LibreOffice doesn’t have as many categories or images, but the images are in color.
Icons and Gallery have some categories in common, and they also have similar graphics. Most of the graphics are different, however.
This means that the two office suites can be used together. If a Gallery graphic is inserted into a LibreOffice document, it will look the same in an Office application. All the features and tools for editing a graphic in Office also can be applied.
The same is true of graphics inserted from Icons in an Office document. The graphics will look the same when they are open in a LibreOffice application. All of the application’s features and tools can be used to edit the graphic.
Most people use Office. Those that don’t yet use LibreOffice can download and use it for free. The price may be worth it just to have the Gallery. More choices may allow users to make better documents.