How to Draw on a Picture in Google Docs

1. With the image selected, click “Insert > Drawing > New” to open the drawing editor over the image.
2. Use the drawing tools to add shapes, lines, text boxes, and freehand drawings on top of the image. These include arrows, rectangles, ovals, straight lines, scribbles, etc.
3. Customize the drawings by changing colors, line thickness, adding borders, shadows, transparency, etc.
4. Position and resize the drawings as needed on top of the parts of the image you want to highlight or annotate.
5. When done, click outside the drawing editor to finalize your annotations on the image.

Some tips:

• Use tight bounding boxes around objects for precision[8].
• Maintain consistency in shapes and colors used across images[16].
• Add labels and text callouts for clarity.
• Group related drawings to keep them together.

So in summary, Google Docs makes it easy to overlay drawings, shapes and text over images to highlight areas or add annotations, without needing additional software or plugins.