To replace the specified text string with image from clipboard in Word, please do as follows:

1. Open the Word document that you will replace text with image, and click the anchor at the bottom-right corner of Clipboard group on the Home page. See the first screenshot below:
 

2. Click Insert > Pictures to insert the specified image into current Word document.

3. In the popping out Insert Picture dialog box, please (1) open the certain folder containing the specified image, (2) select the image, and (3) click the Insert button. See screenshot:

Now the image is inserted in the document.

4. Keep the inserted image selected, and press Ctrl + C keys together to copy it to the clipboard.
Note: After copying the image to clipboard, you can delete the image from the Word document as you need.

5. Click Home > Replace (or press Ctrl + H keys together) to open the Find and Replace dialog box.

6. In the Find and Replace dialog box, please (1) type the specified text string you will replace in the Find what box, (2) type ^c into the Replace with box, and then (3) click the Replace All button. See screenshot:

7. In the popping out Microsoft Word dialog box, please click the OK button to close it.

8. Close the Find and Replace dialog box.

So far, all specified text strings are batch replaced with the image from clipboard. See screenshot:

On the contrary, you can also replace images with specified text string in Word too. Please do as follows:

1. Click Home > Replace (or press Ctrl + H keys) to open the Find and Replace dialog box.  

2. In the Find and Replace dialog box, please (1) type ^g in the Find what box, (2) type the specified text string in the Replace with box, (3) click Replace or Replace All button. See screenshot:

Note: All embedded pictures are recognized as ^g during finding and replacing. If you just need to replace some of images, you’d better click Replace button repeatedly to replace them.

3. In the popping out Microsoft Word dialog box, please click the OK button to close it, and then close the Find and Replace dialog box.

And then you will see the images have been changed to the specified text string already.