Although you can set Windows Explorer to show you the thumbnails of all your pictures, it usually makes it slower to browse through different folders. Additionally it also creates multiple thumbs.db files in each folder and all such files may take up considerable amount of disk space. An alternative to thumbnail preview feature of Windows is adding an image preview in the right-click menu. This can be done easily using the free FastPreview shell extension. It adds an Image Preview in the right-click context menu so that when you right-click on an image file, you see its preview right inside the context menu.
You can download the FastPreview shell extension installer from its website and install it in Windows. After the installation, if you right-click on an image file, it would show an image preview right inside the context-menu. The dimensions of the image in pixels and its color depth is also shown at the bottom of the image preview. It supports all the major image file types like jpeg, bmp, gif, psd, tiff and more.
Additionally, it also adds an extra tab in the File Properties dialog which you can open by right-clicking on an image file and then choosing Properties from the context-menu. You would see an extra tab titled FP which shows a list of various types of EXIF data like software used to edit the image, model and make of the camera used, time and date of taking the picture among many others.
FastPreview shell extension does not offer much in the name of options. You can only set the thumbnail size of the image preview shown in the context menu. By default, this is 300 x 300 pixels which can be customized to suit your requirements. In my personal opinion, the default size is optimal and you should keep it as it is. A larger thumbnail would cover up all your open windows and menus, while a smaller thumbnail might not show any of the details in the selected image.
So if you want a quick image preview feature for your collection of pictures without making Windows Explorer slower, then you can try the free FastPreview shell extension for Windows. The download is available for both the 32-bit and 64-bit editions of Windows.