When developing websites, sometimes (unfortunately), not all assets, such as images, are available. In this case, you can use placeholder images using a service at www.placehold.it. For example, to insert an 350 px wide by 150 px high image, you use the following code:
<img src=”http://placehold.it/350×150″>
Below is how the placeholder image looks
You can also change the color of the image and add text to it dynamically. More information at www.placehold.it