Here is a link with help for all things announcement related - https://help.blackboard.com/Learn/Instructor/Ultra/Interact/Announcements
Adding Images
This procedure is the same for most areas in Blackboard, including assignments, announcements, tests....etc. The way to add an image is fairly universal throughout Blackboard.
Any type of Blackboard content that includes this content editor will allow for inserting images:
And then locate the image you want to attach:
After finding the image, click the Next button in the lower right corner. There are a couple more screens of options to click through and the image will then show in the editor window: