C + Allegro - 253 bytes

#include<allegro.h>
x=-1,y,K=400;float a,h,c,d,k;main(i){set_gfx_mode('SAFE',K,K,allegro_init(),0);while(x++<K)
for(y=0;y<K;y++){for(a=h=i=0;abs(a*a+h*h)<4&&++i<256;k=a,a=a*a-h*h+x*0.01-2,h=2*k*h+y*0.01-2)
;putpixel(screen,x,y,i);}while(1);}END_OF_MAIN()

Output: