It's so easy to over look what Preview is able to do. Drag and drop a folder on Preview, then check out who you can view the folder with the buttons below the side bar, using the Contact Sheet view you can use the slider to change the size of the thumbnails, use the Next or Previous buttons or the arrow keys on the keyboard to scroll photos. Use Preview's Tool menu to crop, change size, Adjust Color, Rotate and flip, also check out the Inspector to see all kinds of info about the photo (Tiff, Exif). I don't know why Apple doesn't have a good tutorial for Preview to help people from over looking it, but so many of the Apps that come on a Mac look so simple that people don't investigate them and start looking for software to download to do the things came on their Mac.