1.Open your WordPress post editor , and upload your image. Then go to the HTML tab, and hit enter to make a space right above your image. Then, write your message there, and add the text you want.
2.Style Your Message. Go back to the Visual Tab and style your text.
3.Place Your Work in the Sidebar
In your HTML tab, copy everything you created. Then go to Appearance-> Widgets tab, and then drag a blank Text widget to the sidebar and paste in your code and Save