An unlabeled photo feels useless at first glance, but it usually carries more information than it looks like it does. A photographer's stamp on the back, the style of clothing, a street sign in the background, or even the type of print paper can help narrow down a decade or a location.
Upload what you have, even the ones you are not sure about. Mention it during your interview - "I have a photo of a family in front of a house, no names on it" - and let the research engine take it from there. Sometimes a single detail in the background is enough to connect it to a place or an event already in your tree.
Do not wait until you have sorted the whole box first. Uploading a handful at a time as you go through them works just as well, and each one adds a small piece to the picture.