Passport and visa photos are often assumed to be identical, and in many cases they are close - but the size, background and even the issuing authority's rules can differ in ways that matter.
A passport photo follows the rules of the country issuing the passport. A visa photo follows the rules of the country you are applying to visit, which may not match your own country's passport photo standard at all. For example, a US visa photo must be 51 x 51 mm regardless of which country the applicant is from.
Some countries that use a light grey or blue background for their own passports still ask for a plain white background on incoming visa applications, since white gives the cleanest result for their scanning systems.
Visa photos are often required to be more recent than passport photos - sometimes within 3 months rather than 6 - since visa applications are treated as more time-sensitive.
Because of these differences, a photo taken for a passport renewal should not automatically be reused for a visa application without checking the destination country's own requirements first. Uphoto lets a new photo be resized to each country's specific requirements separately, in case a passport photo and a visa photo end up needing different dimensions.