Go with IrfanView . It’s the smallest download and easiest to use.

Some versions may require a one-time setup of the "ECW SDK" to enable support due to licensing. 3. IrfanView (with Plug-ins)

Ultra-fast zooming and panning that doesn't lag, even with multi-gigabyte images. 2. QGIS (Open Source)

Enhanced Compression Wavelet (ECW) files are the gold standard for high-resolution satellite imagery and aerial photography. Because these files compress massive amounts of geospatial data into manageable sizes without losing quality, they require specialized software to open.

ECW files store coordinate data internally, so the image "knows" exactly where it sits on the Earth's surface. How to Choose the Right Download