Border image?
Controls
Hopefully it is somewhat easy to understand the tool? You paste an image. Keep pasting to see a few random margin variants.
In the left pane you can edit the offsets so they align with your image. Click and drag the cyan and magenta shaded areas, those are your handles.
The right pane is meant as a preview. You can resize the textarea there, to get a feel for how the border looks at different sizes of thing to contain.
That textarea is also what you can consider the "output" of this tool. The text it contains should be the css to replicate the effect, if you point it at the right image. Ez!
Also, note the "stretch modes" selectable on top of the right pane. It changes the behavior in an interesting way.
Author's note
A thing about me is i don't wanna do math. It's fun to imagine but i don't really wanna do the work. Anyway so css margin image seems powerful AF but finding what values to put is a bit annoying. Maybe a visual aid could help tho - and so here we are!
This is all in-browser, as in, nothing should leave your computer. There's a lot of capabilities in the browser already, i'm trying to lean on these as much as possible. As a consequence this is all pretty simple stuff, all the code is in the index.html... you should be able to save it to your computer and access it that way. For what nefarious purposes i do not know...
Commentar
Note: comments are posted manually when i feel like it. This is all static html baby plus i have other things to do also.