After you have inserted the object, you can change it in many ways. Make sure it is selected (click on it once) to do the following:
The first three options will work with photos/images as well as shapes.
To move it, click on it, hold, and then drag it to the desired location.
To resize it, click and drag one of the little squares that appear in the corners. Hold down the Shift key before you start dragging the corner to keep the image proportionate. Note that depending on the file type, your image may become distorted if you make it bigger.
To rotate the image/shape, click and drag on the circle at the top.
To modify the proportions of a shape, click, hold, and drag one of the yellow squares that appear on the shape.
To change the color (inside or out), use the appropriate Fill (inside) or Outline (line around the image) options in the Shape (or Picture) Format Ribbon or at the right of the Home Ribbon. If you want just the outline of a shape, choose No fill from the dropdown menu.
To add text to a shape, right-click and choose Edit Text…. A cursor appears in the shape - start typing. The text will automatically fit inside the shape. To edit or modify the text (color, size, font, etc.), highlight the text and make the change.
To connect lines between objects, choose a line from the Shapes icon, move your cursor over the object until you see green circles on the edge of the shape. Click and hold on the green circles, drag a line to the other object until you see a green circle again, and then let go of the mouse button.
To change the order of the objects, click on the Bring Forward or Send Backward icon in the Arrange Group of the Picture (or Shape) Format Ribbon – use the arrow next to the icon for more options.
To group objects together, select one, hold down the Shift key on the keyboard and select the other(s), then click on the Group icon in the Arrange Group of the Picture (or Shape) Format Ribbon. When moved, resized, or animated, grouped objects act as one.
To crop the image/shape, click the Crop icon in the Picture Format Ribbon. Cropping handles will appear – move these by clicking and dragging, and the image will automatically be cropped. Note that unlike a program like Photoshop, the cropped portion of the image is still in the document unless you compress the image (as described below). You can get the cropped area back by clicking the Reset Picture icon in the Adjust Group.
To compress the image/shape, click the Compress Pictures icon – this will make your presentation file size smaller. If you have cropped an image, the cropped area is now gone permanently.
To make the background of an image transparent, so it blends to your background, click on the image and go to the Picture Tools Format Ribbon.
Click on the Remove Background icon, then PowerPoint will guess which part of the image to remove (shown below in purple), and bring up the Background Removal Ribbon. This Ribbon allows you to make adjustments to the area that will be removed. This tool does well with single color removal, but it can also work on more complicated backgrounds as well.
You can play with the brightness, contrast, and color using the options in the Adjust Group or modify the shape, border and effect in the Picture Styles Group. Another tool is Artistic Effects, found in the Adjust Group. Move your mouse over preset effects to preview how they would look on your image, and then click on it to apply it.