Replace 'mit_dome.jpg' and 'simple_graph.png' with a default placeholder image

common/lib/xmodule/xmodule/templates/problem/customgrader.yaml

@@ -41,7 +41,8 @@ data: |
               <div class="detailed-solution">
                   <p>Explanation</p>
                   <p>Any set of integers on the line \(y = 10 - x\) and \(y = 20 - x\) satisfy these constraints.</p>
-                  <img src="/static/images/simple_graph.png"/>
+                  <p>You can also add images within the solution clause like so:</p>
+                  <img src="/static/images/placeholder-image.png"/>
               </div>
           </solution>
       </problem>

common/lib/xmodule/xmodule/templates/problem/latex_problem.yaml

@@ -74,7 +74,7 @@ metadata:
 
         Include image by using the edXxml macro:
 
-        \edXxml{<img src="https://courses.edx.org/static/images/mit_dome.jpg"/>}
+        \edXxml{<img src="https://courses.edx.org/static/images/placeholder-image.png"/>}
 
         %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
         \subsection{Example show/hide explanation}
@@ -189,7 +189,7 @@ data: |
         <p>
     Include image by using the edXxml macro: </p>
         <p>
-          <img src="https://courses.edx.org/static/images/mit_dome.jpg"/>
+          <img src="https://courses.edx.org/static/images/placeholder-image.png"/>
         </p>
         <p>
           <h4>Example show/hide explanation</h4>

lms/djangoapps/courseware/features/problems_setup.py

@@ -170,7 +170,7 @@ PROBLEM_DICT = {
     'image': {
         'factory': ImageResponseXMLFactory(),
         'kwargs': {
-            'src': '/static/images/mit_dome.jpg',
+            'src': '/static/images/placeholder-image.png',
             'rectangle': '(50,50)-(100,100)'
         },
         'correct': ['span.correct'],