Unsplasher for Sketch works for shape layers, or symbol instances that have image overrides. Fill with random images or find images using a search term or by specifying a Collection ID.

Photo Grid is a plugin for Sketch that will save you lots of time when you're working with grid layouts.

- Scale and space layers to fit nicely in rows or columns.

- Apply random aspect ratios to selected layers corresponding to common photo sizes.

A handy plugin to help keep your layer list nice and tidy. Select the symbols you want to rename and Symbol Namer will update their names in the layer list, setting them to match the text set in their overrides.