Loading an image directly into Matlab without writing it (temporarily) to a local folder on the server side seems to be impossible. This means you have to make sure your account has the right priviliges on the server side for exporting the images, as well for the database as for the folder to save the images (temporarily).
This is how the query must look like:
% EXPORT IMAGE AND LOAD INTO MATLAB
sqlstringImage=sprintf('SELECT lo_export(tile.image_oid, ...
''/tmp/image_view/%s/%i.png'') FROM tile WHERE ...
image_oid = (select image_oid from tile where ...
id = ''%i'')',<name_db>,ID,ID);
exec(conn,sqlstringImage);
folder=sprintf('Y:/%s',<name_db>);
imageList = dir(fullfile(folder,'*.png'));
I=imread(fullfile(folder,imageList.name)));
% Do your image analysis
....
% Clean temporary file
delete(fullfile(folder,imageList.name)));
The result of the query is only one image, thus imageList in this case only contains one cell array. Probably not the best solution, but it works.