Use "AddPicture" instead of "Insert"
From VBA Help:
Excel Developer Reference
Shapes.AddPicture Method
Creates a picture from an existing file. Returns a Shape object that represents the new picture.
expression.AddPicture(Filename, LinkToFile, SaveWithDocument, Left, Top, Width, Height)
expression A variable that represents a Shapes object.
Parameters
Name Required/Optional Data Type Description
Filename Required String The file from which the OLE object is to be created.
LinkToFile Required MsoTriState The file to link to.
SaveWithDocument Required MsoTriState To save the picture with the document.
Left Required Single The position (in points) of the upper-left corner of the picture relative to the upper-left corner of the document.
Top Required Single The position (in points) of the upper-left corner of the picture relative to the top of the document.
Width Required Single The width of the picture, in points.
Height Required Single The height of the picture, in points.
You'll end up with something like this (Change references as required):
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