Should I be concerned about this mole on the sole of my foot? (Photo)

If you have any concern at all, I recommend having the spot examined by a dermatologist. Routinely, dermatologists perform dermoscopy and serial imaging to assess for worrisome features or changes. A biopsy is often very helpful.

Please consult a dermatologist who can examine your mole and give recommendations for possible treatment.

Even though moles on
the sole of the foot have presumably little sun exposure, there is always a chance any
mole can become cancerous so moles need to be checked regardless of
their location. To be safe, you should be carefully evaluated by a board
certified dermatologist. Please use the ABCDE's as your guide for when to be
concerned about moles: A for Asymmetry; B for irregular Borders;
C for black or uneven Colors; D for Diameter greater than a pencil eraser; and E for
a growth that is Evolving or changing. If necessary, your mole can be biopsied or removed by using a simple "shave" technique which
typically leaves a minimal scar. The mole can then be checked microscopically
for reassurance.

It is impossible to give proper diagnosis from a photo, but in my opinion, moles that appear on the feet particularly, should be biopsied. I know you said that you don't know whether the site has changed or not, but I would suggest you see someone in person who can look at it again, and suggest that you biopsy it for proper diagnosis if the doctor suggests it.