Just get all the files in the directory and keep only the ones with the extensions you want. You could even get the list of all valid image extension from imformats:
%option 1:
extensions = {'bmp', 'tif', jpg'}; %define allowed extensions yourself
%option 2:
registry = imformats; %get all image type supported by matlab
extensions = [registry.ext]; %and get their extensions
allfiles = dir(fullfile(somepath, '*.*'));
isimage = arrayfun(@(f) ~f.isdir && any(strcmp(regexp(f.name, '\.(.*)$', 'tokens', 'once'), extensions')), allfiles);
imagefiles = allfiles(isimage);
for imagefile = imagefiles'
Im = imread(fullfile(somepath, imagefile.name));
...
end
