A means of looking through a folder or everywhere for saved images on the HD by a slide show format

As screen shots, exported JPEGS from Photos pile up and get moved into the Downloads, Document or Picture folders, often haphazardly on the fly, I would like to be able to have an app find these images and present them in a slide format, to see and save or delete images and short vids for use or reuse as attachments for a variety of reasons. Settling in another country, we often have to retrieve and reretrieve document images and photographs of things. It would help in organizing them or getting a quick look through them, faster than clicking on each image one by one or selecting them in groups of 3 or 4. For example we are filing two tax returns and being audited for last years of the foreign country.