(Pictures used below are stock photos and are used as visual examples. I do not own the below pictures.)
(Original Image by Daniel Reche on Pexels)
There are mainly two ways images are used when it comes to marketing and design. They are either used for web or print. Images used on the web are usually lower resolution and smaller in size to allow for faster downloading and less use of internet data.
How about images from Social Media?
The images you would see on a website or social media like facebook, twitter are generally quite small for the reasons mentioned before; these platforms automatically reduce their size when you create a post with images or videos. Hence, images from these sources are NOT suitable for artwork commissions in most cases, especially larger sizes. While they may work for some small sized artwork, they will not give you the best results in the finished pieces. Since the image itself is not detailed enough for the artist to work from, the resulting image will not look highest quality.
Images directly clicked from phone or a camera?
Most modern phones are capable of clicking highly detailed images with stunning resolution. If you have a picture that you clicked with a modern phone or camera, they will be great resolution. These images can be used for both artwork commissions and for printing purposes as well.
The image of the baby you saw earlier shows how a pixelated and blurry image will not allow the artists to see details in important features like eyes properly while the high resolution one will clearly show features like eyelashes, skin folds etc. This also applies to other subjects like wildlife, flowers, architecture etc.
(Original Image by Anna Shvets on Pexels)
Next thing you would want to check in the picture is the colour contrast. You may have sometimes noticed that some images look a bit faded out and you cannot seem to figure out colours in the image. This can happen for various reasons like camera focus, camera lens not being clean, or generally just the way picture was taken (maybe with a bright flash or background was too busy). While most artists have tools and skills to be able to fix contrast, it is best to pick a picture that has good colour contrast. This will make sure the subject of the painting or drawing does not look faded/hazy and is still looking like the main element of the composition.
The image of the baby in yellow here is well contrasted in colour and in grayscale. All elements in the image are well visible and will look good in an artwork piece as well.
(Original images by Anastasia Barth on Pexels)
Lighting plays quite an important role in artworks whether its drawing or painting or any other fine art piece. It adds volume, depth, and movement to the composition. Its extremely important that the image reference you provide has the subject in good lighting. If the subject is too much in shadow, the important features of the subject will not be visible to the artist and hence, the artwork will also represent the same. If the image is overexposed, the subject's features again will not be visible to the artist and the artwork piece will reflect the same. Some artists are able to work around lighting issues but to get the best results in the artwork and reduce the stress on the artist as well, choose a picture where your main subject is well visible. If you have a uniquely photographed picture and like way the lighting is in the picture, you may even check with the artist and see if it makes a good artwork piece.
The images of the woman above are examples of how lighting can influence the way an artwork turns out. While both the images are high resolution, the lighting in the left one does not show all of the subject's features and the artwork will also reflect the same. The image on the right shows the subject's features in light and hence, would make for a clear portrait drawing.
(Original Image by Edu Carvalho on Pexels)
For composition, you may work alongside the artist to figure out what's the best way to place the subject in the artwork. This may mean suggesting the artist to remove the background, crop the picture a certain way, remove unwanted objects, zoom in, zoom out, or rotate the image a certain way. This can bring the artwork to a whole new level. Artists have a great vision for composition so bring it up with them on how the image may be used to get the best artwork composition. Most artists do this themselves but having an idea on what items in the artwork you'd love highlighting and what items you do not feel are important will help you in selecting the image reference to the artist.
The image of this elderly woman has been adjusted on the right to show you how composition can change the way an artwork piece will turn out. The left is a great photograph and is well detailed. However, for a commission, the image on the left is highlighting the overall theme and would not look as effective since there are a lot of competing elements in the picture. The picture on the right is zoomed in a bit and allows the portrait of the lady to be the main focus of the composition. Hence, the picture on the right would make for a better portrait drawing or painting.
These are the few things that I believe will get you the best results for an artwork commission. If you are unable to provide a reference that works, you always can check directly with the artist and figure what's possible. If not, it may be helpful to ask the artist to help you with clicking a good picture.
Hope this helps!