How resources are grouped into <ItemGroup> s in a .csproj file

Question

In my file, .csprojimage resources are inside tags <ItemGroup>.

<ItemGroup>
  <Resource Include="2b.png" />
  <Resource Include="Resources\foo1.png" />
  <Resource Include="Resources\foo2.png" />
  <Resource Include="Resources\foo3.png" />
</ItemGroup>
<ItemGroup>
  <Resource Include="bar.png" />
</ItemGroup>
<ItemGroup>
  <Resource Include="Image1.png" />
</ItemGroup>
<ItemGroup>
  <Resource Include="cam.png" />
</ItemGroup>

Why are some of them in their groups, while part? Is it just an artifact of automatically generated XML or does it mean something?