What Markdown is
A Markdown table is rows of pipe-separated cells with a dashed rule under the header. Alignment is set by placing colons in that rule.
README files, GitHub issues, documentation sites, Obsidian and Notion.
What JPEG 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 Markdown to JPEG
Leading and trailing pipes are optional and both are handled. A pipe the author escaped with a backslash is read as data rather than a column break, which is the usual reason a hand-written table parses one column too wide.
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 Markdown to JPEG
Markdown records 2 things about a table that JPEG has no way to hold.
Nothing in JPEG records that the first row is a header. It is drawn at the top and looks like one, which is all that is left of the distinction.
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 Markdown if you will need the values again.