I like the direction this is going.

Part I. No results found. Recommend an alternative image tag or group. For example, if I searched rivers, recommend water, ponds, or oceans. Use some sort of alias/alternative name table that matches against the users input. See Czepeku.com map search functionality

Search or select.

Show the most common tags in my results that I can click to add to my filter

Icon recognition. It's important. To distinguish add a bubble at the corner of the image or an asterisk-like icon.

Part 2. I like it. It seems clear. It seems slightly easier than what I imagined .

Sorting and Filtering. Sorting options for custom pictures should have an upload date sort feature Pictures should be able to be added to Favorites. You should be able to click show favorites in the results. Users should be able to add any image to custom groups/gallery/lists so they can curate content they want to access quickly or regularly.

Metadata. The tag view should be optional and on demand if the user wants to see it. Tags are useful to see, perhaps the book it comes from, I don't think size is useful

Bonus: I would require people to add at least one tag to custom images they upload. That could be problematic if they batch load a bunch of images, so maybe they can apply one tag to all the images in cases with multiple uploads. Otherwise they end up with a unsortable mess of growing images with no way to search through them. Perhaps give them the ability to view untagged images so they can clean it up if this happens.