I think JS libraries such as gif.js and gifplayer.js can display specific frames of a gif. So possibly you could create an animated gif whose frames are your portfolio of images, and so you could retrieve n images using your lone n-frame gif image.

CSS Image Sprites https://www.w3schools.com/Css/css_image_sprites.asp

You could do that with blobs and client code...or use mjpeg movies...im not aware of multiple images as such though...itd be worth researching multipart mime types i think

Could you transmit multiple images in a zip file?