https://www.google.co.uk/advanced_search is a really good place to start. By filling in the boxes you can include words or phrases in the search or exclude certain words. This should make it easier to improve a search.
When searching for images in Google make sure you click on search tools as this then gives more options. For instance if a large file is required so that it doesn’t pixelate go to size and choose large. If you need a clipart image then the google hits can be narrowed down by choosing clipart on the Type drop down menu. If you require a transparent background so that the image can be inserted onto a patterned or coloured background then choose transparent from the colour drop down menu.
You will notice that there is a drop down menu called usage rights. The work done by children is non-commercial so selecting the non-commercial use with modification would be appropriate.
If you are using Bing to find images you have access to MS Office clipart. There is an extensive set of menus to narrow the search including a license menu. Children may have tried to insert an image in a MS application (eg word) by clicking on the Online Pictures icon. They will have seen a message saying that the search results are licensed under creative commons and that they should check that the license of the image they choose complies with their needs.
Children need to know that they are responsible for respecting the rights of others’ property, including copyright. They will probably have some knowledge of this in connection with films and music but may not realise that it extends to text and images. At this point it is worth mentioning “Creative Commons”. It is widely held that it is necessary to use Creative Commons images to comply with the law. CC is an organisation with a highly respected licensing system; they seek to make it clear when images may be used and modified freely. Websites like behold and photosforclass will only return images that CC have labelled as available for reuse and modification so are really easy to use to ensure that the results can be used. However, by making an appropriate selection in either Bing or Google it is also possible to comply with copyright responsibilities.