Other pictures showed the masked men, who wore armbands in the colours of the Bulgarian national flag, hunting for migrants in the forested border area.
The paramilitary group Ms Festerling joined on patrol is one of several believed to be operating in the Turkish-Bulgarian border area, independently of Bulgarian security forces.
The group hands over any illegal immigrants it captures to the police.
Ms Festerling boasted on her Facebook post of braving “Scorching heat, rough terrain, jungle-like forest and mosquitoes” which “ensure these patrols are anything but a walk”.
She claimed that 1,000 migrants cross the border illegally each day, and said discoveries of “fresh rubbish and dumped clothes” were evidence of illegal immigrants in the area.
The photos showed masked vigilantes holding up crushed soft drink cans, empty medicine packets with Arabic labels and Arabic identity cards.
“The most popular brand among the invaders on their robbery and rape campaign is Red Bull,” she claimed.
“So much for the do-gooder speech of supposed ‘asylum-seekers’,” she wrote. “These are ice cold and calculating warriors of Islam, who come from decayed cultures and do not want the least to do with our free, decadent lifestyle, but despise it,” she wrote.
Pegida, or Patriotic Europeans against the Islamisation of the West, first emerged in Ms Festerling’s home city of Dresden in 2014. It has spread across Europe and brought tens of thousands of people onto the streets at its height in early 2015, but has fallen in prominence in Germany after a series of scandals involving its leadership.
Ms Festerling, a former candidate for mayor in Dresden, shot to international fame in February when she called for asylum-seekers to be shot.
“If they keep crossing the border and you cannot arrest them, shoot them,” she said.
Her far-Right opinions have proved too extreme for Pegida, which expelled her a month ago after she called for the German people to “take up pitchforks” against Angela Merkel’s government.