Building a photo mosaic generator - that uses Flickr

after looking at some of the cool pictures that are made from a mosaic of photos i realized that the only thing amazing about them is the sheer amount of information they contain. after all, if you have all the photos stored in an organized data structure, the creation of the mosaic is some pretty basic image processing.
then i realized, why not have something that reads from a large image aggregator, in particular, flickr, and use the results to create an arbitrarily large piece of mosaic?
the choice of language to do this for me would be java, considering that it would be cross-platform, and i am somewhat adept to image processing in java, in comparison to c++ or javascript.

this mosaic generator would roughly have these divisions:

PhotoStream class: responsible for fetching the image data based on a set of parameters; probably uses flickr api to do this
ProcessPhotoStream class: processes the photo data fetched by the PhotoStream class. Maybe sort the photos by average color and store them into a map with a key value of an arraylist of the bufferedimages that has the corresponding color.
ProcessMosaic class: processes the image to turn into a mosaic. Resizes it to an appropriate size and decrease the amount of colors in the image.
CreateMosaic class: take the data returned by ProcessPhotoStream and construct an image that looks like the original image from them. If more image is required(not enough colors), it will call PhotoStream/ProcessPhotoStream again.


Things to watch out for:
long loading/processing time of PhotoStream means a lot of optimizations will need to be made.
Resizing/processing images requires a shitload of processing.