Apostille
An "apostille" is a form of authentication issued to documents (e.g. diplomas) for use in countries that participate in the Hague Convention of 1961. The function of the apostille is to identity any stamp or seal affixed to an official document certify the authenticity of the signature on the document, and the capacity in which the person signing the document acted.
Check here if country where your diploma was issued participates in the Hague Convention. Otherwise you will be asked to legalize your diploma in the Polish consular office in country in which it was issued.
Recognition of a secondary school certificate
Your certificate can be recognized on the basis of international agreements.
Recognition Procedure
If your certificate does not come within any international agreement, its equivalence with a relevant Polish school certificate can be stated only by nostrification.
Recognition of diploma
If your diploma gives access to further studies (MA studies or PhD studies) in a country where it was issued, it gives the right to study at a given level (MA studies or PhD studies) in Poland. Note that your diploma can also be recognized on the basis of international agreements.
Recognition of Diplomas
If your diploma does not give access to further studies in a country where it was issued, you have to have your degree nostrified.
Nostrification
Nostrification is a process or act of granting recognition to a degree from a foreign country. It means that foreign educational qualification is compared to its Polish equivalent and stated as equivalent. The nostrification of the secondary school certificate is conducted by Kujawsko- Pomorskie Kuratorium Oswiaty in Bydgoszcz.
Note: Diploma/school certificate must be nostrified by the end of the first semester.
Here you find the list and addresses of the local educational authorities.
More information here.
https://www.gov.pl/web/edukacja/recognition-of-foreign-school-certificates-and-diplomas-in-poland