Image Viewer
The Image View window is where you inspect every image the model carries — source textures and baked results alike — and assign one to a material's PBR layer. It's a floating, non-modal window: the 3D viewport stays fully interactive while it's open.
Opening it
Three ways in: the sidebar's View: Images button, the icon toolbar's Image Viewer icon, or the I key. Escape closes it. Right-clicking any image inside the flat canvas also opens an Image Info popup showing the same info panel described on Image Info & Assign to Material — a third way to reach it, not a separate feature.
Two-part layout
A fixed-width left column holds the Source and Generated Texture lists on top and the current image's info panel underneath. The rest of the window is a canvas showing the flat UV/image view for whichever entry is selected.