Graphologist IsraelImaging and preservation
Lossy JPEG compression may introduce blocks or halos near sharp dark edges. Saving the image repeatedly may alter more detail. PNG can preserve the pixels of the image it receives, but converting a JPEG to PNG cannot recover detail already discarded.
If you have both the phone photograph and a copy sent through a messaging app, retain both. A mark around a numeral that appears only in the compressed copy should be compared with the phone image before being attributed to an alteration of the document.