Change editor button images
 

We want to change the image for our image upload button in the editor from the "tree" to a camera. I thought I could do this most simply by just changing the contents of the file named insertimage.png in the images/editor folder.

However, doing that does nothing on my system. I have not yet tried disabling all the add ons, etc. but have been flushing all the cache elements I can find. Can anyone point me to where these images are protected? Are they automatically stored in a sprite cache?

I thought I could just let it age and it would eventually come in, but it has been about a week now and still no change.

It's possible you modified the wrong image.
In Chrome, press F12 to open the developer tools, click on the network tab and then filter on images. Now go to your page which contains the image you want to modify and press CTRL + F5 to reload the page, you should see a bunch of requests in your developer tool, find the image you want to edit and look at the location.

All those button images are in images/editor/sprite.png. I verified the tree image is in there. It's odd that that one image you replaced is there by itself all lonely.

I am sure I can (and should) find this out for myself, but how does one replace a sprite image?

If you look at the sprite image you'll see there are three versions of each image. The most faded corresponds to the disabled state for the button; I'm not sure about the intermediate one. So first you would have to use photoshop or equivalent to make faded versions of your image and then carefully copy (or "clone") in your own images over the top of the existing images. If you get it correctly positioned, down to the pixel, it will work. The only alternative I know is to generate a whole new sprite image but to do that you would need every one of the other images, and then you would have to replace the css somewhere to match up with the new image.

What I suggested here is doable if you have a good photo/image app and are willing to do some trial and error with positioning.