We recommend you upload full-resolution images/videos to benefit most from what PhotoDeck has to offer, as the system automatically generates the preview images on your website. If you are not planning to deliver the images digitally (e.g. if only for portfolio display), and if you don't wish to upload high-res files, uploading 3000px-wide images will you the best long-term flexibility.
The max image file size allowed with your plan is indicated in the upload window.
Images are best left not sharpened (or only very slightly sharpened as part of e.g. the RAW conversion process), so that your clients keep full flexibility in the printing process.
To save on disk space and upload times, we find that high-quality JPGs (rather than TIFF images) are suitable for most applications.
In most cases, images are resized automatically. For license purchases that specify a size in pixels or a file size (e.g. Royalty-Free, Rights Managed Web uses), the buyer gets an image exactly the size purchased. For low-res downloads, we deliver an 800x800 pixel image that has your watermark applied, if it was applied upon upload.
In all other cases where a digital file has to be delivered, we deliver the high-resolution image you have uploaded, without modification.
All preview images are converted to the sRGB color space, so you can safely upload high-resolution images in the space of your choice (e.g. AdobeRGB), as long as you embed the profile.
Note that for performance reasons (page display speed), the sRGB profile is not embedded in the thumbnails, so the color will be accurate only on the larger previews (assuming the viewer's browser is properly color-managed).