Honestly, I would also advice against the idea of trying to use Coda as an Image storage/gallery.
Other the fact that Coda wasn’t build for that purpose, images are actually not necessarily well treated by Coda (there are some inconsistencies here and there but I’m confidant in the fact that it might get better at some point 
) .
For example, in the doc I’m currently building, using an Image field in a table and uploading more than one picture in that field, when wanting to see the pictures in full view, it opens a lightbox with a carousel but the images are cropped instead of fit and there’s no other way to “admire” the picture in its full view (well, you can click on it, but the carousel won’t disappear and you’ll need to scroll through that picture). Just this already doesn’t feel as a great gallery.
Still in a table, and still using an Image field if you just add one picture in that field, it shows perfectly but you won’t have any way to really link it to other pictures (by a lookup or other).
In this example, the pictures are exactly the same ones, except for the way I have them in that table.
The pictures in the Text field are coming from another table (using a LookUp field) where they are stand alone pictures (one picture per row in an Image field).
Even grouped in this field, because they’re gathered there from a formula, they’ll still act as stand alone pictures. If you click on one of them, it will shows up in a lightbox but you won’t be able to switch between them. And if you ListCombine() them, you’re getting back to square one with an intrusive carousel and cropped pictures.
There might be ways to go around all this by using Image URL fields instead of Image fields, but then it would mean that you’re already storing your pictures elsewhere, using a service that might be more appropriated to create a gallery.
And putting pictures just on the canvas to create some kind of gallery there can be a pain as you can’t put them there freely and (re)organize them easily. (There’s not easy way to place them side by side or resize them).
It might do the work for few images though but it’s not the most practical way.
That’s also just my opinion .
I know Coda might be tempting, as there are actually no clear limit in storage, but with the upcoming files and attachments feature, that might change.