The picture may be contained in the cell of a table – especially if the author used copy and paste to put it in your document.
Float your pointer to the top of the page and see if a downward-facing solid black arrow appears, which indicates the entire page is part of a table (sometimes, it’s the entire document – cells are not outlined/invisible). From there, you can convert table to text and the image will become selectable.
NOTE: This is often the problem when you change format in one place and it affects formatting elsewhere in the document unexpectedly. It’s a real danger with copying and pasting.
If this doesn’t help, center the image (if it fits) on your screen and hit Alt+PrtScr (printscreen), paste from the clipboard to MS Paint, and crop out all but the picture. Now you can work with it however you want.