I fit into images.json this way:
minecraft: textures / gui / title / progressBars.png
But progress bar loaded from jar file mod.

And further. What did change in version 1.3.8?

I moved the file from jar BTS file progressBars.png and tossed a file Forge.
And in the file path images.json changed. Minecraft is the path to the texture of the Forge or resoursepack

Ok, that does sound strange

Sorry. Everything works correctly

Are you trying to change the text inside of images.json, or are you creating a progressBars.png file somewhere? (And can I have the text inside of images.json if you did change it)

Also you need to override "betterloadingscreen:textures/gui/title/progressBars.png" instead of "minecraft:" (if that's what you are trying to do)