Image gallery tips
Prepare images for upload
In order to upload assets to the customizer gallery, the images must be first separated into individual files. Typically, this comes up when receiving stock images from an asset library:

A stock Illustrator file with a number of assets composited together on one artboard
Some assets may be applicable only to a specific personalization type. For example, laser engraving files typically require a pure black/white image asset without halftones. An image like the one below would need to be avoided when setting up laser engraving:

Depending on the type of the source file, the preparation flow may differ.
Using Adobe Illustrator
Open the file in Illustrator
Select the desired icon (which may be multiple vectors) and Group them together
Using Pathfinder panel, use Merge tool to flatten the design:


Make sure that the tool have not introduced any artifacts
Add the selected group to Assets panel
Either drag the group the panel
Or right click on the group and click Collect for Export → As Single Asset


Using the Assets panel, set up the desired export format
For Illustrator assets, that would typically be SVG
Select all collected assets and Export