iphoto. Can a section of a photo be partially deleted ?

I do not remember, how it could be done in iPhoto 3, that is a very old version. But all versions of iPhoto had a retouch brush, afaik. Look for a retouch tool in the edit tools.

Could it be, that you are using Photos 3 on macOS 10.13 High Sierra and not iPhoto3?

In Photos 3 you can use the Retouch tool to brush away the number plate. See this link: Retouch a photo to fix marks and blemishes in Photos on Mac – Apple Support (UK)

1. In the Photos app  on your Mac, double-click a photo, then click Edit in the toolbar.
2. Click Adjust in the toolbar.
3. In the Adjust pane, click the arrow  next to Retouch.
4. Drag the Size slider to select a brush size.
5. After dragging the slider to select a brush size, you can also change the brush size by pressing the Left Bracket ( [ ) and Right Bracket ( ] ) keys.
6. Position the brush over the mark, then click or drag across the mark to remove it.
7. If the mark is small and isn’t removed on the first try, try zooming in to make finer changes.
8. Tip: If you’re not getting the results you want, you can copy pixels from another part of the photo and apply them to the blemish. Press the Option key while you click an area that has the texture you want, then use the retouch tool to apply the change. Control-click the image and choose “Clear manual Retouch source point” to stop copying pixels from the area.

In more recent versions you can use the MarkUp Photo editing extension to draw across the number plate.

Great. You're welcome, Brian. 😊