How to Create a Great Thumbnail

• Plan what objects to insert into thumbnail
• Use a Good background remover https://www.remove.bg/upload
• Upload image of object (likely comes with undesired background)
• Edit > "Erase/Restore" tab > Erase (remove any spots that should be erased)
• Edit > "Background" tab > Color > select Transparent background
• Download object with transparent background
• Pick a bright, attractive Background. Example: "Ray burst", labelled for reuse with modification 

https://www.google.com/search?q=ray%20burst&tbm=isch&hl=en&hl=en&chips=q%3Aray%20burst%2Cg_1%3Abackground%3AgqWbAy1flvc%3D&tbs=sur%3Afmc&ved=0CAEQpwVqFwoTCICy2tGSvOgCFQAAAAAdAAAAABAC&biw=1522&bih=710

https://pixabay.com/images/search/ray%20burst/

• Use inkscape to put together
• Drop background file into Inkscape work area. Show document borders through the background if desired (File > Document Properties > Page > Border > Border on top of drawing)
• Drop object with transparent background into Inkscape work area. 

How to insert a (e.g. white) border around an object which is already has a transparent background (method does not involve time-consuming tracing)
1. Image should have a solid object with transparent background. You can achieve it by using this https://www.remove.bg/
2. Path > Trace bitmap (Shift+Alt+B) > select image > Update > set Threshold to 0.99 only (dont set to 0.999....) > Update > OK
3. Edit paths by node (F2) > delete whichever nodes which shouldn't be there (usually just delete nodes within the black shape). The black shape will eventually be converted from a bitmap image to a vector.
4. Fill and Stroke window (Shift+Ctrl+F) > "Fill" tab: (No paint) > "Stroke paint" tab: (Flat color, WHITE) > "Stroke style" tab: (width: 22px)
5. "Export PNG Image" window (Shift+Ctrl+E) > Export area (Page) > Export as (decide path) > EXPORT