Hopefully you are creating your form with content controls rather than legacy form fields. This would make the forms easier and faster to process when they are returned, and then you can also use a building block gallery content control for the images.

Save your form as a template. Insert the pictures into the template and size them as required. Select each in turn and press ALT+F3. Save to the current template in the Custom 1 gallery in a new Category 'Pictures'.

Delete the images from the document. Then insert the content control at the required location and point it at the Custom 1 gallery > Pictures.

Then when you click the dropdown, you will see the pictures you have saved, from which to select.

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Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com