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src/_includes/welcome.md

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                     <p>We will take applications such as climate change and show how you can participate in the big open source community looking to find solutions to challenging problems with exposure to github and parallel computing.</p>
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-                    <img src="https://user-images.githubusercontent.com/6933510/136199652-0a1275ad-8452-4c9b-ac68-d33ed22f1d17.gif">
+                    <img alt="An interactive lecture about climate economics. You can see the user moving the global CO2 emissions in one graph, and a second graph with global temperatures over 200 years responds." src="https://user-images.githubusercontent.com/6933510/136199652-0a1275ad-8452-4c9b-ac68-d33ed22f1d17.gif">
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                     <p>You will learn mathematical ideas by immersion into the mathematical process, performing experiments, seeing the connections, and seeing just how much fun math can be.</p>
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-                    <img src="https://user-images.githubusercontent.com/6933510/136203450-f1d38de6-f43c-4bfc-a987-f954e7a9da2e.png">
+                    <img src="https://user-images.githubusercontent.com/6933510/136203450-f1d38de6-f43c-4bfc-a987-f954e7a9da2e.png" alt="An image of prof. Philip the Corgi, but the whole image is swirled and twisted using a mathematical transformation. Overlaying grid lines are also twisted, showing the non-linearity of the transformation.">
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                     <p>Our course material is built using real code, and instead of a book, we have a series of interactive <em>notebooks</em>. <strong>On our website, you can play with sliders, buttons and images to interact with our simulations.</strong> You can even go further, and modify and run any code on our website!</p>
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-                    <img src="https://user-images.githubusercontent.com/6933510/136196607-16207911-53be-4abb-b90e-d46c946e6aaf.gif">
+                    <img src="https://user-images.githubusercontent.com/6933510/136196607-16207911-53be-4abb-b90e-d46c946e6aaf.gif" alt="An interactive lecture about the Newton method. A parabolic function is graphed, and we use sliders to control the number of iterations of the Newton method. Each iteration shows a tangent, demonstrating the algorithm.">
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                     <p>In literature it’s not enough to just know the technicalities of grammar. In music it’s not enough to learn the scales. The goal is to communicate experiences and emotions. For a computer scientist, it’s not enough to write a working program, the program should be <strong>written with beautiful high level abstractions that speak to your audience</strong>. This class will show you how.</p>
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-                    <img src="https://user-images.githubusercontent.com/6933510/136203632-29ce0a96-5a34-46ad-a996-de55b3bcd380.png">
+                    <img src="https://user-images.githubusercontent.com/6933510/136203632-29ce0a96-5a34-46ad-a996-de55b3bcd380.png" alt="A snippet of Julia code defining a new type called Sphere, with fields 'position', 'radius' and 'index of refration'.">
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