graphics

When you insert a graphic, visit the Arrange tab, and set text wrap to None. This causes it to remain fixed. However, depending on how you want that graphic to interact with its surrounding content, such as wrapping text around it, you may find that another of the text wrap settings may be what you need.

Again, depending on your choice of how the graphic should interact with the rest of the document content would determine if it should be locked, and the choice of Object Placement and Text Wrap settings chosen.

You can try locking the selected graphic from the Arrange panel by first setting Object Placement to Stay on Page and then Lock. You won't be able to lock the graphic while Object Placement is set to its default: Move with Text.