Interpretation of picture of human chromosomes
The picture can be a bit misleading because it represents 22 autosomes (autosome = non-sexual chromosome) while there are 22 pairs of autosomes (so the homologous chromosome is not represented). And it represents the whole pair of sexual chromosomes (the individual is a male). 

homologous chromosome

For each autosome represented, there is another one which would be its homologous chromosome.

Sister chromatids

As you can see, each chromosome looks like an X. The right and left side of this X there are chromatids (two chromatids per chromosome here). The chromatids are attachedf by the centromere. 

Note

Please note that 1) chromosomes looks like they are represented here only during the metaphase (when they are condensed). 2) A chromosome is not always made of two chromatids. Sometimes it is made of single chromatid only. It depends on the moment in the cell life cycle.