Shulchan Oruch Horav 90 (22) advises against davenning in front of decorations on the wall of the shul. Is it, therefore, a good thing to use a picture of the Western Wall as a “mizrach” ("mizrach" refers to an ornamental wall plaque used to indicate the direction of prayer in Jewish homes).
The relevant quote from Shulchan Aruch Harav is as follows (my own translation):
בגדים המצויירים שתולים בכותלי בית הכנסת לנוי אע"פ שמן הדין אין בהם משום חציצה אין נכון להתפלל כנגדם כדי שלא יהא מביט בציורם ולא יכוין בתפלתו ואם יקרה לו להתפלל נגדם יעצים עיניו וגם כשמציירים כותלי בית הכנסת נכון שלא לצייר ציורים נגד פניו של אדם אלא למעלה מקומת איש.
Pictures that are hung on the walls of a synagogue for decoration; although they are not considered a "separation", it is nonetheless not correct to pray in front of them, to avoid looking at the illustrations and lose concentration in his prayers. If he happens to pray in front of them, he should close his eyes. Similarly, when decorating a synagogue, it is correct not to draw pictures at eye level, but rather they should be placed above the height of people.
It seems quite clear from the words of the Shulchan Aruch Harav that this is a practical recommendation - it's not advisable to daven in front of things that will distract you.
This is the way the Lubavitcher Rebbe seems to understand the law. He writes in a letter (Iggres Kodesh vol. 10 pg. 137) that a possible justification for those shuls which do not follow the above and do have decorations, is that people who frequent the shul will not become distracted since they are already used to the decorations. He compares this to the law by Birkas Cohanim, that although a Cohen with physical deformities may not recite the blessing because it is distracting to the people present. However, if the Cohen is well known in the city it is permitted since he will no longer attract their attention. However the Lubavitcher Rebbe concludes that nonetheless this is not advisable, since newcomers may pray in the shul and get distracted.
It therefore stands to reason that if such pictures of the Kossel do not distract the person davening in front of them (or even cause him to think about Yerushalayim etc.) this would not be a problem. If however, he will spend the duration of the davening admiring the artistic techniques of the painter it is surely not correct to pray in front of them.