First, go to options -> users -> manage users and groups . Create a new group called "Image" and put the username or email of the people you want to give the permission of upload images.
Then, go to:
1- At the bottom of your app->Edit this page.
2- At the engine wheel -> "Search for macro" .
3- Macro by name -> search for "editor_insert_image_button" .
4 - editor_insert_image_button -> "override this macro" .
replace with this code
<override_macro name="editor_insert_image_button">
<n.if.visitor.is_in_group group="Images">
<then.overridden/>
</n.if.visitor.is_in_group>
</override_macro>