coordinate system - How to use PROJ4 to reproject a file

Unfortunately, GDAL does not support a particular projection I am trying to achieve (the ob_tran rotated pole projection), so I am trying to use PROJ4 to convert a geotiff file to the projection I want.

However, I am not sure what the correct syntax for such an operation is. Using the command:

invproj -m 57.2957795130823 +proj=ob_tran +o_proj=latlon +o_lon_p=20 +o_lat_p=20 +lon_0=180 input.tif

I get only a lot of gibberish in the console, such as:

133d13'9.044"E  62d0'32.793"N  -32767
133d13'9.044"E  62d0'32.793"N  Band1
133d13'9.044"E  62d0'32.793"N
133d13'9.044"E  62d0'32.793"N
133d13'9.044"E  62d0'32.793"N� �D�k�����������k�R�f�����P�w��B�����|�[�=�$

This is not due to the particular projection I am trying to use. Trying a normal Mercator projection with the command:

proj +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +units=m +k=1.0 +nadgrids=@null +no_defs input.tif

I also get a lot of gibberish.

0.00    -0.00�4�L�}�z���`����)�,�$��������
0.00    -0.00��6�������G�R�f�@�
0.00    -0.00
0.00    -0.00�
0.00    -0.00���������3���<�����;
0.00    -0.00�����

What am I doing wrong? From looking at the manual, I thought I need to put the name of the file(s) at the end of the command line, but apparently, that is wrong?

How do I convert a file to another projection with PROJ4?