I noticed that the postcard photo doesn’t look a lot different from Main Street in Blackfoot today, so I grabbed a Google Streetview capture for comparison. It’s below the postcard.
If you follow with your finger straight down from where Main Street is printed on the postcard, you can just make out where Bridge Street intersects with it. Both buildings on either side of Bridge are still there today though the one on the far left has been much modified. Both have 45-degree corner entrances, though that’s difficult to make out in the contemporary photo.
Working back toward the right you can still make out the next two buildings, which are little changed. Then we see that the next three buildings in the 1909 photo have a metal facade tying them all together in the contemporary photo. Past the 1910 Groceries building we see a single gray building with a distinctive cornice running along the top. In the contemporary photo we see that part of the façade of that building has been modified to make it look like two distinct buildings.
The first photo was probably taken from near the train station, which is today the Idaho Potato Museum.