To add a logo to invoices you would go to Settings > Locations > Click edit pencil beside the location > Click the Upload Logo button. From here, upload the photo and click Save when you are done. Now going forward, that logo will be on your invoices, statements, reports, etc.

If you have chosen Use Main Company Info on Reports (found in Settings > Locations > Edit Location > Checkbox), then you would go to Settings > Company Info > Click the Upload Logo button. From here, upload the photo and click Save when you are done. Now going forward, that logo will be on your invoices, statements, reports, etc.