You may notice that the men in these photos look more European than North African/Arabic. Algeria was a hot bed for piracy and the Barbary Slave Trade, where European Christians were captured at sea or by raids. It was also a place European pirates could find safe haven, if they converted to Islam. The most famous of which was the English pirate Jack Ward, whom Jack Sparrow is supposedly based on. There were around a million European slaves in the 17th century, many of whom were freed after converting to Islam as well and going on to be important member of society.
The Barbary Pirates attacks led to the USA fighting their first major war in the Arab world.
The pirate raiding in the Mediterranean is a particularly interesting subject. For the vast majority of navies in the Mediterranean, galleys essentially use manpower as an expendable resource. Galleys are needed to raid and to power galleys, you need captives from raids, so it’s a self perpetuating need.
The Christians also raided across the Mediterranean, but the Muslims were undeniably more successful. One of the major driving forces for conflict between the Knights of Rhodes/Malta and the Ottoman Empire is that the knights frequently raided the water routes used for the Hajj and as the defender of Islam, the sultan obviously needed to respond.
There are many possible reasons for the Muslims dominance in piracy in the early periods. One of which is that the reconquista’s ethnic cleansing forced a lot of Spanish Muslims into western North Africa. This provided a population that were familiar with their raiding targets in Spain and had grudge. The Muslims also benefitted from a more unified purpose, with the pirate states and the ottomans having similar goals (the pirate states were often ottoman vassals, too), while the Christians, despite Hapsburg dominance, were just as likely to be in conflict with each other. The Venetians, despite multiple famous conflicts with the ottomans, were just as likely to trade with them, much to the frustration of other Christian states. Infamously, the French even offered Muslim fleets access to French ports to fight their common enemy of the Hapsburgs. Muslim raiding was so catastrophic along the Mediterranean that whole communities would be depopulated in Italy.
As Cyten mentions, there was the possibility of advancement for non Turks and converted Christians, with several of the most famous pirates and admirals belonging to this group. Hayreddin Bararossa was Greek and born to a Christian mother and became one of histories most successful pirates and later grand admiral of the ottoman fleet. Occhiali/Giovanni Dionigi Galeni was an Italian that was captured as a galley slave, but converted to Islam and became a successful Corsair, later admiral, and commanded a portion of the Ottomans fleet at Lapento.
