How can I post photos to my course page?

Go to the course where you want the image to appear. Select the "Insert a label" from the "Add a resource or activity" menu. (A label is a Resource.)
Inside the textbox for the label, click on the "Insert Image" icon from the list of formatting icons. (The icon is probably in the third row, 8th from the left). In the page that appears, click on the "Find or upload an image." When the "File picker" program appears, choose the "Upload a file" option. (If you have already posted the file, you can select it from the "Recent Files" option. Click on the "Browse" option, find the picture on your computer, give it a name (it is good to give it the same name, including extension, that you have on your own computer), click on the upload button, and then click on the "Insert" button. You can add text or other pictures to this label.

You can change the size and alignment of the image by clicking on it and dragging one of the "boxes" or using an option from the format bar.
Save the "label" you have just created and check to verify that everything looks the way you want it to look.

Using an image that is on-line on another web page:
Find the URL (web address) of the image. This address will be different from the web address of the page displaying the image. This can usually be done by going to the web site and (if your mouse has right and left click) right-clicking on the image and selecting "Copy image location."
Go to the place on the course page where you want the image to be displayed. Select the "Insert a label" from the "Add a resource" drop-down menu.
Inside the textbox for the label, click on the "Insert Image" icon from the list of formatting icons. (The icon is probably in the third row, 8th from the left). Paste the image location into the line for the image URL. You probably will need to supply some text describing the image for people who are visually handicapped and can't see the screen.
You can change the size and alignment of the image by clicking on it and dragging one of the "boxes" or using an option from the format bar.
Save the "label" you have just created and check to verify that everything looks the way you want it to look.