Above the edit box where you type, there are some icons. The green and brown frame icon lets you insert/embed an image in your posting and be visible immediately.
The paper clip icon lets you attach files, like m files, mat files, xlsx files, and even image files. Though if the image files are attached this way they have to be downloaded and loaded into a program to be seen - they are not seen immediately like if you use the green and brown frame icon.
It's also worthwhile to read this tutorial: http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup
