Polyester film base support into which ultraviolet light absorber is kneaded and image-forming element

A base support comprising at least a transparent polyester film into which an ultraviolet light absorber has been kneaded, wherein the ultraviolet light absorber is at least one kind of ultraviolet absorber represented by the following general formula (1):

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• wherein X1, Y1, and Z1 each independently represents an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, or a heterocyclic group, which groups may each be substituted or unsubstituted, with the proviso that at least one of X1, Y1, and Z1 represents a substituent represented by the following structural formula (A):
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• wherein R1 and R2 each independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an aryl group, an alkoxy group, an aryloxy group, an acyloxy group, an alkylthio group, an arylthio group, an amino group, an acyl group, an oxycarbonyl group, a carbamoyl group, a sulfamoyl group, a carboxyl group or a salt thereof, or a sulfo group or a salt thereof, which groups may each be substituted or unsubstituted, and adjacent R1's and R2's may join together to form a ring.