Stoked 3.5 has linked images to variants.
Here's how I do it quick and easy. Let's say you have a t-shirt with s/m/l/xl and that t-shirt has various colors, say white/black/green.
1. Start fresh and add a new product.
2. Fill in the usual stuff, but before you save check "this product has multiple options"
3. Fill out values while hitting tab, something like this. Be sure to upload your imagery at the same time
4. Save your product
5. Now click the color you want to update, click bulk actions, update images
6. Rinse, repeat for each color.
7. Marvel at the glorious magic of auto image swapping with variants.