The harbour on the front of a postcard may seem to explain the object. Turn it over, where permitted, and a different story can appear: who sent it, what they chose to mention and how the card travelled.
Work from your own card or a collection image that shows both sides. Transcribe a short message before interpreting it. Keep spelling as written, mark an unreadable word, and distinguish printed captions from handwriting.
An invented example makes the problem clear. A card depicts a sailing ship, while its message says only “Arrived safely on Tuesday.” That sentence does not establish that the sender travelled on the pictured vessel. The image and the personal message may be connected more loosely.
Compare three dates if available: a date written by the sender, the postmark and a catalogue’s date for the photograph. They need not identify the same event. Avoid assigning an undated photograph the date of a later message without further evidence.
For your notes, make one line about the pictured scene and another about the correspondence. Add a third for the unresolved connection between them.
That small separation preserves the postcard’s appeal while preventing its attractive image from doing more historical work than the evidence allows.
Editorial illustration from this site’s image library; not documentary evidence of the example or object discussed.