Qt toBase64 and Linux base64 differs - c++

Question

Subj. Why can it be?
I've tried all the flags for Qt toBase64 but nothing changed.
Bash:
cat Invader_1.png | base64
Output: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 BYBiAgDFBACKCQAUEwAoJgBQTACgmABAMQGAYgIAxQQAigkAFBMAKCYAUEwAoJgAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAHAn3wG6mDu8
W58tNgAAAABJRU5ErkJggg==
Qt:
QImage image;
image.load("/home/undead/Pictures/1489180309_Invader_1.png");
image.save(&buffer, "PNG");
buffer.close();
bytes_array = bytes_array.toBase64();
Output:
iVBORw0KGgoAAAANSUhEUgAAAQAAAAEACAYAAABccqhmAAAACXBIWXMAAAsTAAALEwEAmpwYAAADQklEQVR4nO3cwW3bQBRF0edAhagUuhKrlLgTu5KwFHbibGIgiyBIMhNx7HcOMEuNPknhQtxMAgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAJxjS_I2YW33HbvKFs9oqi9nDwCcRwCgmABAMQGAYgIAxQQAigkAFBMAKCYAUEwAoJgAQDEBgGICAMUEAIoJABQTACh2OXuAhRxJnift9XXw80eSl-Ep1nJLch3cY8-cZ3RM2AN-ac_4iTX7nWe-hz3uy3K8AkAxAYBiAgDFBACKCQAUEwAoJgBQTACgmABAMQGAYgIAxQQAigkAFBMAKCYAUEwAAJJsGT-wwvoYawtJ_AOAagIAxQQAigkAFBMAKCYAUEwAoJgAQDEBgGICAMUEAIoJABQTACgmAFBMAKCYAECxy9kDTHJLch3cY_Tz716THIN7XJM8DU-ylpXuyy3jh4IcSV4G92CSPeefMjPztJltgetwX36_9gnXczqvAFBMAKCYAEAxAYBiAgDFBACKCQAUEwAoJgBQTACgmABAMQGAYgIAxQQAigkAFBMAKPZw8vdvSb6dPAOc6TEnHi7iHwAUEwAoJgBQTACgmABAMQGAYgIAxQQAigkAFBMAKCYAUEwAoJgAQDEBgGICAMUEAIpdzh5gktckx-Ae1yRPw5PwEfi9LGJL8jZhbQvNYq2_tozbFprln3kFgGICAMUEAIoJABQTACgmAFBMAKCYAEAxAYBiAgDFBACKCQAUEwAoJgBQTACgmABAMQGY7zHJg_Vf1uNfPAf-gABAMQGAYgIAxQQAigkAFBMAKCYAUEwAoJgAQDEBgGICAMUEAIoJABQTACgmAFBMAKDY5eTvP5I8T9pnxh4zZtl-rBW8ZPzeXJPcBveYZc_n-70cE_ZgIXuSt0XWNuF6tgWu433tE66Hn3gFgGICAMUEAIoJABQTACgmAFBMAKCYAEAxAYBiAgDFBACKCQAUEwAoJgBQTACgmAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAcCffAbqYO7xbny02AAAAAElFTkSuQmCC

Answer 1

You are comparing 2 different things.
cat Invader_1.png | base64
Outputs the base64 binary content of Invader_1.png.
While
QImage image;
image.load("/home/undead/Pictures/1489180309_Invader_1.png");
image.save(&buffer, "PNG");
buffer.close();
bytes_array = bytes_array.toBase64();
Converts 1489180309_Invader_1.png into a pixel image and back to a PNG and then outputs the base64 binary content of the new PNG.
And as stated by #JustRufus and #TobySpeight, a PNG of the same image can be created with different settings (e.g compression levels) and/or metadata leading to different binary contents.
If you want to compare things you should fix your Qt code to just read the file:
QFile file("/home/undead/Pictures/1489180309_Invader_1.png");
file.open(QFile::ReadOnly);
QByteArray data = file.readAll();
file.close();
data = data.toBase64();