What JSON is
JSON is a text format for nested data: objects with named keys, arrays, strings, numbers, booleans and null. It has no date type and no comments.
Every web API, most configuration files and anything that talks to JavaScript.
What JPG is
A lossy image format designed for photographs, where losing a little detail in a gradient is invisible.
Places that will not accept a PNG upload.
What changes when you convert JSON to JPG
Four shapes all read correctly: an array of objects, an array of arrays with a header row, an object of column arrays, and an object keyed by row id. A single wrapper key holding the array, which is how most APIs reply, is unwrapped automatically. Nested objects are flattened one level into dotted keys; anything deeper is kept as JSON text in the cell, because a table cannot hold a tree.
The same render as PNG, saved as JPEG. It is the worse choice for a table and it is worth knowing why: JPEG compresses by discarding detail around sharp edges, and a table is nothing but sharp edges. Letters get a visible halo and hairline rules blur. It also has no transparency, so a background colour is always painted rather than left clear.
What carries over from JSON to JPG
JSON records 4 things about a table that JPEG has no way to hold.
JSON knows which of its values are numbers. JPEG keeps only their appearance, so nothing downstream can sort or sum them without someone reading them back off the image first.
An empty cell and a missing one are the same thing in JPEG, so a null and an empty string in the JSON both come out blank and can no longer be told apart.
JSON can hold a value that is itself a list or an object. JPEG has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
JPEG is the end of the line for this data. Reading the table back out of it is a separate and much harder problem than writing it, so keep the JSON if you will need the values again.