You can also change images per content version.
Images is the spreadsheet are set by URL. Some spreadsheets allows for formatting so the image appears in the spreadsheet itself. Refer to the spreadsheet docs for more info.
As an example, you may have something like this in your spreadsheet:
Select the layer you'd like to sync and press Pull > Spreadsheet Pull. You can do a Quick Pull if you have already pulled the data.
Once pulled, you will be prompted to confirm the updates. The update will preview the image update:
Pressing update will update the image in the design!