Update README.md

Replace GIFs with JPGs because GIFs were not loading properly on GitHub's README preview.

README.md

@@ -17,15 +17,15 @@
 </h1>
 
 <p align="center">
-  <img src="https://olive-groves.github.io/butterfly_registrator/images/registrator_registration.gif" alt="Animated screencapture of the Butterfly Registrator showing a control point of a moving image being moved to match that of a reference image, the registration being applied, and the sliding overlay preview being moved to compare the registered image with the reference image.">
+  <img src="https://olive-groves.github.io/butterfly_registrator/images/tutorial/batch_start.jpg" alt="Screenshot of the Butterfly Registrator showing control points on a reference image and moving image, with the registered result previewed in a sliding overlay.">
   <br />
   <i>Registering an XRF element map to a color image¹</i>
 </p>
 
 <p align="center">
-  <img src="https://olive-groves.github.io/butterfly_registrator/images/registrator_alphascale.gif" alt="Animated screencapture of the Butterfly Registrator showing an XRF map dragged into the alphascale converter, the color picker selector being changed, and the save alphascale shown in the Butterfly Viewer.">
+  <img src="https://olive-groves.github.io/butterfly_registrator/images/tutorial/alphascale_color_picker.jpg" alt="Screenshot of the Butterfly Registrator showing the alphascale converter.">
   <br />
-  <i>Alphascale conversion of grayscale XRF element maps¹, then shown in <a href="https://olive-groves.github.io/butterfly_viewer">Butterfly Viewer</a></i>
+  <i>Alphascale conversion of a grayscale XRF element map¹</i>
 </p>
 
 Butterfly Registrator is a preprocessing app for aligning images using pairs of control points you click and drag. It helps you align (or [*register*](#how-does-the-registrator-register-images)) images to a given reference such that their heights and widths match and the features within those images line up, making it easy to later overlay and compare them without the hassle of manually zooming, stretching, and cropping them beforehand.
@@ -62,4 +62,4 @@ Our [Butterfly Registrator page](https://olive-groves.github.io/butterfly_regist
 
 ### [Developers](https://olive-groves.github.io/butterfly_registrator/butterfly_registrator.html#developers)
 
-Or see the source markdown file in the `docs` branch under `docs/DEVELOPERS.md`.
+Or see the source markdown file in the `docs` branch under `docs/DEVELOPERS.md`.