A rough rule of thumb is that the dots should not be resolvable by the
human eye at the preferred viewing distance. This translates roughly to
something like:

Minimum viewing distance (in inches) = 2000 / dpi

For ideal identical dot sizes in continuous tone printing. Roughly
equivalent to an ideal eye resolution of cleanly separating two black
dots with one pixel inbetween when the angle subtended at the eye is 3'
arc (or 0.001 radian).

We can haggle about the constant in practice. In strong light I can
resolve the pattern in a halftone 600dpi laser print at about 10" so a
more conservative estimate might be

Min viewing distance (in inches) = 6000 / dpi

And not all dots are created equal - especially in CMYK halftone
rendition where unlucky clusters of dots with a range of sizes can be
visible at larger distances.

Regards,
Martin Brown

Do you mean printer dots or pixels per inch. There is not a clear
answer for the measure of printer dots, but for pixels, the pixels
should subtend significantly less than a minute of arc for the distance.

i dont think so, wait and your answer will come

IMHO looks like a multiple exposure to me or a long exposure with
multiple flash strobes (redeye ?) or something deliberate.