Using the python gdal module to open images in the same projection but different sizes

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I'm using the gdal.Open() module on python 2.7 to open Landsat GeoTIFF images. They have the same UTM map projection, but different image sizes.

How do I fix the image sizes to be the same? I'd like to make direct pixel-by-pixel comparisons.

gdal_translate can be used simply to change the size of an image using the -outsize parameter, which takes two integer values as the xsize and ysize respectively, or two percentage values to scale the image. see here

gdal_translate -outsize newxsize newysize imageFile outputFile

You need to reproject all rasters to the same raster shape/size. You can do this with gdalwarp to each raster file, e.g.:

gdalwarp -te xmin ymin xmax ymax -tr xres yres -r resampling_method srcfile dstfile

You can optionally replace -tr (target resolution) with -ts width height to specify the number of rows/columns.

The -te (target extents) and -tr/-ts (target resolution/size) options forces each of your source raster to have the same raster shape overlay, so you can correctly do a pixel-by-pixel comparison. You also need to choose a suitable -r resampling method, depending on what your analysis is trying to achieve.