How to replace a photo in a Word document automatically when I take a new photo

If you copy a given photo to the folder the document is in and name it, say, 'Birthday.jpg' (assuming it's a jpg pic) you can then insert that photo into your Word document via Insert|Pictures>This Device. Select the photo and choose the 'Link to File' option from the insert dropdown.

From now on, whenever you replace the photo with another one named 'Birthday.jpg', Word will update the document to show that photo. Be sure also to configure Word to update fields before printing.

When Word inserts a picture from a file, it usually sizes it to fill as much of the page as possible while maintaining the correct aspect ratio. A useful trick if you want to constrain your photos to fit within a given area is to create a single-cell table with a fixed height and width to where you want them to go, then insert the photo into that as outlined above. Any picture inserted into such a table will have its dimensions constrained to fit the space available, at the correct aspect ratio for the picture. To set the fixed:
• row height, use Table Tools>Layout>Properties>Row>Specify Height>Exactly.
• column width, first uncheck the 'automatically resize to fit contents' option under Table Tools>Layout>Properties>Table>Options. Then set the preferred column width under Table Tools>Layout>Properties>Columns.
You might also want to set the cell margins to 0 all around. It's also a good idea to format the cell paragraph with 0 before/after spacing.